He used to cheat

How does that saying go? A cheetah never change their spots? I wouldn't put yourself through that emotional pain because every day you will wonder everytime he takes his phone with him when he doesn't come home on time, what he's doing when out with his friends. As someone who got back with their partner after they grovelled for weeks and promised he could change, the change lasted all of 2 weeks and hes gone back to hiding his phone and taking it everywhere with him, hes gone back to barely helping round the house. It's not worth the emotional pain trust me

My partner cheated and begged me back for a year. We got back together and he’s proved to me he has changed for now- if that lasts who knows but I am hopeful

All I can suggest is they have different threads or groups (depending on what platform) “are we dating the same guy” etc. and people look through and or post their men or experiences with serial cheaters. Our intuition usually lets us know, but I totally understand needing definite proof. I do think people can change in time if they really want to. I see a lot of times for men it seems to takes a lot longer imo. I know love and relationships are hard to shake, and I totally get giving somebody a second chance, but if they show you who they are again please believe them. You’re young and beautiful and don’t need to waste your time on anybody who doesn’t respect you like you deserve. Wish you the best of luck!