Advices please

So me and my ex broke up like a month now and he’s in the new relationship with someone for about 3 weeks

We have a child together he comes up to see the child.

While the child was sleeping while he sat downstairs to keep an eye on her while I was sorting my bedroom out and he came up started play fighting with me. Then 10 mins later he started getting all touchy with me as he put his hands down my pants touch my private part and then he apologised that he shouldn’t have done that while he’s with someone else. Then proceeded to drag me on top of him moving my waist up and down. Obvs I got off and then he apologised.

I told him it’s best that he tells the new girl what he did but he doesn’t consider that cheating. He wants to pretend nothing happened.

What should I do?