Kenobi is a sociopath whose whole job is to ruin the life of Luke and everyone connected to him. After leaving his father to burn to death, he brought Luke to a desert planet and basically abandoned him in a place with no cover, where the Empire was sure to find him and kill him eventually without any chance of escape. When Luke finds Ben instead, he lies to convince him to kill his own father. While they split up, nobody notices Obi Wan finding Leia and sleeping with her, then disappearing before the others get to her. Obi Wan is not killed by Darth Vader, but rather used force teleport and fled the scene naked. Before teleporting, Obi Wan glances knowingly at Leia and her father, although Luke thinks it’s him he’s looking at:
Rey is born between the films IV and V, but Leia never tells anyone (we already know that Obi Wan can be very manipulative) and Obi Wan takes Rey shortly after her birth and spends the next few years hanging out on Dagobah with her and Yoda (hence the British accent). He teaches her a few rudimentary lessons in the force and also helps Yoda to train Luke before getting tired of caring about other human beings and abandoning her on another desert wasteland.
After ROTJ, Luke finally pieces together how screwed up the relationship with Obi Wan really was, especially after Leia finally tells him her secret (about this time, he also realises that Obi Wan’s ‘ghost’ was just a cheap hologram trick and ‘Darth Vader’ in the cave was just Obi Wan screwing with him again). Of course the other hope Obi Wan was talking about wasn’t Leia, it was his own daughter - Obi Wan was far to narcissistic to care about Leia at this point and he even tries to stop Luke from helping her on Cloud City.
Luke returns to his sister and her family and tries to make things better, but after years of substance abuse it’s obvious that he is not able to control his own life, let alone train his nephew in the force (it’s becoming increasingly clear that little Ben isn’t benefiting from this relationship either, and that name is really getting to Luke). Eventually he gets rid of the lightsaber he was given by Obi Wan (which just symbolises the start of a really bad time in his life) and disappears; nobody knows where he’s been for years. You can imagine how he feels when his niece turns up with the damn thing in her hand:
