luke’s entire motivation as a character is his desire for a family that will truly love him. when he’s young, he fixates on the image of his dead father as the ultimate role model who would have supported and nurtured him, who would have basically been everything that uncle owen wasn’t. that’s why it’s so devastating for him when ben dies, bc ben was the first adult to really actively provide him with any kind of help or support. and that’s why he tries so, so hard to redeem anakin; he cannot let go of the idea that if things had turned out differently, anakin would have been the perfect father luke always imagined him to be.
luke also seeks out very close friendships/relationships with his peers: biggs and the tosche station kids, and then han and leia, and then wedge and all of the other resistance pilots. he’s a very openhearted person to begin with, but that’s not the only reason that he clings so tightly to his friendships. he is trying desperately to find a family for himself. but this doesn’t work either: biggs dies, and wedge dies, and dack dies, and han and leia have each other and don’t need him (or so he thinks by the end of rotj). luke’s despair at the end of the original trilogy is profound. he has failed to achieve his primary objective as a character, to find a group of people who will dependably love and support him.
so then he tries something else. he tries to re-build the jedi order. maybe by cultivating that community, by being father he wishes he had had to a new generation of force-sensitive kids, he can find some kind of belonging. but then, of course, his school is destroyed by his own nephew. the skywalker family continues to tear itself apart. luke blames himself: he thinks that by using leia’s son into for his own ends he has destroyed any chance that she had to escape the cycle of revenge and bloodshed. he doesn’t know that leia doesn’t blame him at all, or how desperately she wants her brother at her side. he doesn’t know that han cares about him so much that he spends a decade combing the galaxy for any trace of his old friend. having seen so many people he loves die, luke thinks the kindest thing to do is remove himself from their lives completely.
(btw speaking of the greek tragedy style curse of the house of skywalker, remember how that guy at the beginning of tfa says “you can’t escape the truth that is your family” and kylo agrees with him? ben solo is just as invested as luke in carrying on his family’s legacy, he’s just focusing on a different part of it. he, too, wants a community that will give him something his family can’t. he just goes about finding it in the wrong way.)
anyway this is why luke’s relationship with rey is going to be so important!!!! rey and luke want the same thing: a family. imo episode viii is going to give him the chance to finally, finally, after all these years (canon and real-life) resolve his narrative and find the family he’s been looking for all his life.
What about Beru, though? Even if you figure that Owen wasn’t a good father figure to Luke (and I’m not sure I really buy that, either) I can’t believe that she didn’t love her adopted son, or that Luke didn’t know that she did, or that she wasn’t his family 100% even though they weren’t blood related.