deciding what to do after he cheats

You cannot accept his infidelity as a “slip”, because it wasn’t a one-time incident. Slips are moreso accidental f*ck-ups . A slip-up is when a man’s drunk and has a one night stand, or he has a no-strings-attached hookup after you guys argue. Additionally, slips are unplanned and usually come with lots of regret. (Not that this makes things acceptable.) What he had was a consistent series of trysts with another woman. He deliberately lied to you each and every time he was going to see her as well, making this anything but a “mistake.” If anything, the fact that he got caught acting a fool with this woman is the mistake.