As I was watching the sequels (again-) I can see how Ben/Kylo gets progressively more interested in Rey. He's never really like hurted her in anyway to get rid of her, as he could have done that easily. snoke connected their brains, making them "see" eachother more. and as Rey sees him more, and he sees her more, their both more calm. I think he turned to the good side 1. because it was right and 2. for Rey, He loved Rey, he never really tried to kill her, and literally even saved her/ tried to help with palpatine. I thought it was so cute when they kissed cause he seemed at peace, he was happy to hold her and be with her. And he died saving her. A true romantic relationship could have been formed