Infidelity Advice

My partner was caught 3 years ago talking to and lying about this woman. I know they exchanged pictures. We’ve been trying to work through it since. I recently saw a post saying that guys don’t pay attention to the little details if they don’t care. I know I shouldn’t of asked bc it hurt my own feelings, but I just needed to know if he cared about the pictures. I asked what color of underwear it was in and he knew right off the top of his head. 3 years ago… how would y’all feel in this situation? Should he of remembered the color after 3 years? Advice please and please be kind. I’ve been really going through it…