We're talking about a grown ass man, breh.
Dude wanted to live his adult life like it was some Disney movie despite it being obvious that his girl was playing the field, that's 100% on him.
Love makes people do stupid things, always has, always will. Ask a abused woman, why don't she leave her abuser/husband/partner, she will say 'I love him and he doesnt mean it, he just gets frustrated at times'. Obviously she is a grown ass woman, she can leave whenever she wants but doesn't. He may kill her, she knows this but chooses not to, because she's holding on to something that has since long passed. That's Candido and Sunny, he was holding out for her to be that teenage girl he met all those years ago.
Sunny was probably the first bit of p*ssy he ever had, hopefully it wasn't the last, for him and he couldn't let it go.