This is my interpretation of Cain

I always liked the idea that being reincarnated would fuck you up in some way. Like you experience death and rebirth in a body with a brain that's still develloping so you can't process your though and emotion the way you used to and you can't really vocalised it or talk about it to someone. Plus you know you're different from everyone else so you'll always feel isolated in some ways.
The concept is'nt really touch upon in this story, I just like the idea in general.

I like to think Cain subconsciously put every repressed issues he had onto his affection for Diana. Like she's one of the few things that ground him to this reality. Rather than thinking about the implication of being reborn, of what he wants to do in his life, of how he feels about about his past life or anything he just put everything into his goal of taking care of her.
The fact that his parents didn't really take care of him didn't help. I think Cain lacked emotional attachement and support, like something/someone to love and someone to love him. I think as a kid a part of him craved for it. He didn't even notice it, as a reincarnated being he probably though he was fine and didn't need anything. And so he emotionaly latched onto Diana, really badly.

This is just me overthinking for fun.
It's just more headcanon than anything but you know ... FUN ! ヾ(❀╹◡╹)ﾉ~