Shavonne is smart as hell, he knows what he signed up when he asked him out, he knows the consequences and what hes risking though. Where is shavonne even going to go? Yeah common sense he should leave no duh, but this isn't your typical heesu in class two fluff. Its possible to have a happy ending even if the story has a ML who is a psychopath (the beast must die as an example)
and your quote, "And in this case it turns out to be Shavonne, a poor lonely guy next door. That's probably why he piqued Lewellyn's interest" this is actually wrong. I bought the raws and you'll see more into why Lewellyn is so stuck on Shavonne (its their past when Shavonne was a prison guard)
That's a psychopath for you. He's manipulative. And he doesn't 'love' Shavonne, his definition of love is twisted. He just wants someone who'll only look at him, who'll only have him. So that he can possess that person like an object. And in this case it turns out to be Shavonne, a poor lonely guy next door. That's probably why he piqued Lewellyn's interest. He took advantage of his loneliness like he said. He used his charm and good looks to draw Shavonne to him. Then he helped him, showed kindness. This are all the common tropes of a psychopath. Like a psychopath said "If you want people to trust you, offer them help, get to know them." That's how they take advantage of people. On top of all that he kills people without guilt(if what Shavonne thinks is really true).
No matter how cute, kind, charming Lewellyn may seem Shavonne's not gonna get anything good out of it, it's only a momentary pleasure. Shavonne should get the fuck out of there and as soon as possible.
Honestly I find Lewellyn cute too but his actions are really disturbing.