Partner makes me feel so stupid

So i found out he cheated back at start of relationship in first year bull crap thought i was seeing my ex

I have kids etc n trying to make it work we start couples counselling this week

We argue today as i say i dont believe when he says it happend when pregnent she says baby was already here

He says soon as soon was born he changed

Anyways as i bought it up today he says im pathetic and all i do is go on and on and on and he should split with me as hes been punished enough