The relationships of Kylo Ren.
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 struggled 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.
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 became known as Kylo Ren and his by his fellow Jedi (as they would later become members of the Knights of Ren) who were some of Luke's own apprentices he had turned, he killed 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, while Ren went on to terrorize the galaxy as a leader of the First Order.
Luke was the only one who managed to survive and escape the Jedi massacre. In the aftermath of the Jedi massacre, Luke was deeply grieved and wracked with guilt, blaming himself for his students' deaths, Ben and his other students' turn to the Dark side.
Luke then mysteriously disappeared 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. Ben probably had a good relationship with his maternal uncle; prior to the Jedi massacre.
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.
Ren and Rey have been enemies ever since Rey located and purchased BB-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 for the time being. 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 manipulation by Snoke.
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. Though she tried to return him to the Light side and even fought beside him against Snoke's guards, Ren refused to join her and instead tried swaying her to the Dark Side to no avail. He also vowed to destroy her when she refused to join him and in so doing, snuff out the Jedi for good. As such, they remain enemies.
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, partly due to his lack of Force-Sensitivity, and 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.
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). He eventually turned him to the Dark side, and anointed him with the name of Kylo Ren. Ren still serves 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 and kill him. Ren then assumed the role of "Supreme Leader" for himself.