The relationships of Kylo Ren/Ben Solo.
Ren apparently had a poor relationship with his father, calling him a disappointment. He rejected Han and brutally murdered him, though he deeply regretted this almost immediately after it occurred, showing that he did at least had some love for him prior to turning to the dark side. It's shown that Han's death actually has haunted him and made him very unwilling to do the same to his mother, Leia, even damaging his faith in his master Snoke.
Not much is known about his relationship with his mother; however, Ben likely had a loving relationship with Leia. Prior to his fall to the dark side - when he started to struggle with his inner darkness - Leia was terrified that he might end up like his maternal grandfather Anakin Skywalker and so - sent him to study under the tutelage of her brother, Luke.
Unfortunately, Luke was indirectly responsible for Ben falling to the dark side, when he made a mistake by contemplating and nearly considering killing him upon sensing how strong his connection to the dark side of the Force is. This proved to be extremely disastrous, as Ben became known as Kylo Ren. Leia was heartbroken that her son had become evil and mourned his fate bitterly. Yet, despite all the atrocities that Ren had committed over the years, Leia still believed that Ben could come back to the light and be redeemed. After Ren killed Han Solo, she lost the believe that there was good left in him and declared her son an enemy. Despite this, when he was given a chance to kill her, he couldn't bring himself to do it, shedding tears of remorse and guilt for even considering killing his mother.
When Ben started to struggle with his inner darkness, he was sent to study under Luke's tutelage at the request of his mother, Leia, in the hope of preventing him from ending up like his maternal grandfather, Anakin Skywalker. Luke taught Ben of the ways of the light side of the Force and lightsaber combat and they once had a good relationship, with Ben being known as Luke's most prized student and his favorite.
Unfortunately, Luke made a mistake by contemplating and nearly considering killing him upon sensing how strong his connection to the dark side of the Force is. This proved to be extremely disastrous, as Ben's former faith in his uncle was shattered and he tries to defend himself from his uncle atempt murder by colapsing the hut there are in. Later, Luke wakes up to find that his Jedi Temple has been destroyed. The destruction of the Jedi Temple kills most of Luke's apprentices; this act greatly delayed his uncle's plan to restore the Jedi Order to it's former glory and left his uncle despondent. Meanwhile, Ben went to meet Snoke as there was no one left of his family he trusted since he also felt abandoned by his parents. He then assumes the Kylo Ren persona and goes to terrorize the galaxy as a leader of the First Order.
In the aftermath of the destruction of the Luke's Jedi Temple, Luke was deeply grieved and wracked with guilt, blaming himself for his students' deaths, Ben and his other students' disappearance. Luke then went to hide into exile; as he embarked on a quest to seek out the First Jedi Temple. Ren, under the orders of Snoke, is instructed to find and kill Luke. Snoke knows that as long as Luke is alive, a new generation of Jedi Knights can rise once again. Ren himself resents Luke for trying to kill him and was constantly bitter when talking about Luke when he connected with Rey and believed his uncle would just toss her aside like he did with him.
They finally met when Ren was on the verge of complete victory over the Resistance. Ren showed his rage towards his uncle by shifting from being initially mocking to soon showing hatred when he looked at Luke as they fought, though astonishingly despite remaining calm and focused, Luke showed some remorse for failing Ren but coldly said that he would not even attempt to save him. Luke was successfully able to anticipate that Ren's rage towards him would hamper his ability and mind, although even had Ren fought at full clarity, he most likely wouldn't have beaten Luke anyway. Being Ren's teacher in lightsaber combat, he was obviously far more skilled and experienced than his hot-headed nephew, and used this to his advantage, tricking Ren into fighting with him while the Resistance escapes, after easily dodging all of his nephew's attacks, openly showing how had he wanted to, he could have killed him many times over, Luke finally revealed his deception once sensing Rey had finally saved the Resistance and before dying, he taunted Ren one last time as Ren could do nothing but accept his failure in anger.
Anakin died before Ben was born. However, Ben come to greatly admire and revere his maternal grandfather's power, but, also came to fear that he may never be as powerful as the Chosen One. This fear and his desire to live up to his grandfather's legacy was why he, like his maternal grandfather before him, turned to the dark side, becoming known as Kylo Ren. Over time, Ren came to admired more of his grandfather's dark aspects then his light aspects, and came to regard Vader as his true-self. Ren has (seemingly) become far worse then his grandfather; although Vader was brutal and ruthless, he did (genuinely) care about his family, as he never killed a member of his own family in cold blood, not even for power, ultimately leading to his redemption. Ren on the other hand was willing to kill his father to keep from feeling such feelings as love and compassion from making him feel weak and pull him back to the light side.
Ren became enraged when Finn and Rey respectively used his grandfather's lightsaber against him, as he believes that the weapon rightfully belongs to him.
Friends and Allies
Although they both serve the First Order to destroy the Resistance and conquer the New Republic, Ren does not get along with Hux at all, partly due to them both trying to win the approval of Snoke and mainly because Hux's arrogant, rude, short-sighted, and delusional traits, Ren once threatened Hux, stating that if he ever pushes him too far he will kill the latter without hesitation, Hux on the other hand, dislikes Ren in part because of his hot-headed temper, and in part due to the scientifically inclined Hux having little patience for "mysticism" regarding the Force.
Tensions between them grew when Ren killed Snoke. Though he did not know Ren had murdered his master, Hux tried to kill Ren regardless so as to try and claim power for himself. However, Hux, regardless of ambition, was swiftly put into place when Ren used the Force to choke him into submission. Ren also was more abusive towards Hux afterwards, slamming him into a wall with the Force when Hux angered him during the battle of Crait.
EnemiesBB-8. Ren is very convinced of her power, believing even she does not know it. He very much longs to turn her to the dark side and train her, but this ultimately backfires. Rey's hatred of him increases after he kills Han Solo, and she tries to kill him with Anakin Skywalker's lightsaber. Rey left him for dead but later developed a Force bond with him that was the result of them being a Dyad in the Force.
Through this bond, the two formed a legitimate emotional connection and Ren became very fond of Rey, as she was one of the few people to ever treat him with compassion and kindness after his fall to the dark side, to the point she even began to refer to him as Ben. As their connection strengthens they start to feel empathy towards each other through a shared sentiment of loneliness, and they try to comfort the other through their bond. Through their interactions, they also show signs of a growing attraction towards each other.
When Rey went to meet him in the Supremacy in an attempt to convince him to turn to the light, Snoke reveals that he had manipulated their bond to lead Rey into a trap and orders Ren to kill Rey. Instead, Ren kills his own master saving her life. Though she tried to return him to the light side and even fought beside him against Snoke's guards, Ren refused to go with her and instead he pleaded her to join him in the dark side to no avail. He also vowed to destroy her when she refused his offer and in so doing, snuff out the Jedi for good. However, later Ren saw her again through their bond and seemed depressed about her rejection contradicting his earlier vow about ending her life. As such, they remained enemies but with a clearly complicated relationship.
Even after being rejected in Snoke's Throne Room, Ren continued to pursue Rey determined to turn her to his side. When the Emperor offered him power and a fleet in exchange for Rey’s life, Ren immediately betrays him planning to take the Throne of the Sith together with her. After their duel on Kef Bir, Ben renounced the Darkside and went to help Rey that had gone to confront Palpatine alone. Though he was gravely injured by the Emperor, he survived long enough to find Rey’s lifeless body as the result of her confrontation against her grandfather. Shaken by her death, Ben decides to sacrifice himself by giving her the rest of his own vital force to restore her life. He succeeds in doing so and, after she wakes up, they stare and smile fondly at each other before giving in to their feelings sharing a kiss. Shortly after, while still in her arms, he succumbs to his wounds becoming one with the Force.
Ren and Finn have been enemies ever since he captured Rey and killed Han Solo; Ren became enraged when Finn uses Anakin Skywalker's lightsaber against him. When he states that weapon belongs to him, Finn tells him to come and get it (unaware that Ren is in fact Anakin's grandson, and Ren feels that that lightsaber rightfully belongs to him) and the two engage in a lightsaber duel (as Finn was trying to avenge Han's death) although he is able to hold his own reasonably well for a relatively short period of time and even manages to lightly wound Ren's right shoulder. However, ultimately, Finn is defeated by Ren, mainly because of the latter's superior experience and skills in lightsaber combat, as Ren disarms him of Anakin's lightsaber and deals him a severe wound to his back. In fact, the only reason Finn was able to last that long against Ren without any experience in the Force was that Ren was injured and was grieving for Han, had Ren been fighting at full strength he would have likely had no trouble at all killing Finn.
Kylo and Poe become enemies when Ren and the First Order capture him and Ren forced Poe to reveal the location of the Map of Luke Skywalker in BB-8 by using the Force to make him reveal it.
Snoke met Ben by unknown means and was deeply interested in him due to his embodiment as a focal point of both light and darkness (which was unusual for a Knight of Ren or any practitioner of the dark side of the Force to be attracted to). After Luke's Jedi Temple's destruction, Ben feels abandoned by his family and goes meet Snoke as he had nobody else that he trusted. He then turns Ben to the dark side and anoints him with the name of Kylo Ren. Ren served him loyally, believing that the Supreme Leader was wise and right to overthrow the New Republic.
Ren was (initially) unaware that Snoke did not truly care about him, as he was only using Ren for his power. However, due to the trauma and conflict from killing Han, Ren began to doubt the dark side as well as Snoke, which eventually caused the dark warrior to grow to lose faith in his master.
The increasing doubt Ren feels towards Snoke is even more aggravated when he starts to interact with Rey through their Force Bond. The relationship he develops with Rey is something Ren comes to be very fond of, so when Snoke reveals that he had manipulated their bond and starts to torture her in front of Ren, he looks furious at his master. Thus, when Snoke orders him to kill Rey, he chooses to save her and kill his master instead. Ren then assumes the role of "Supreme Leader" for himself.