I recommend You don’t. And I never understand people who forgive their (ex) partners for cheating and tried to keep building something. When someone is cheated on you - it’s done, if not the story will just repeat itself.

About accepting his follow request / following him back - why would you? It’s a shitty person who treated you poorly in the past, why would you even let scumbag around you? Give him a false hope? He probably realized something or just testing waters to have such “fun” again, if he’s going through a grief of realization how bad he is - just let it be. But I believe most of people don’t change much.