She is clearly willing or already has strayed. I think the most prudent thing to do is to end things. Shit between you two is already tainted. Even if you try and work things out you will always have trust issues. No matter how much it hurts, leave her be and let her figure her shit out. The most important thing for you to do is try and make sure that everything between you and her is civil. Not because she deserves that, but for the kid. I think it is much better for you two to separate and be able to give your child the most stable environment possible, than to have a caustic relationship that the child will witness and internalize. Sorry that you have to deal with this. Cheating/betrayal of trust always sucks. You just need to make sure whatever you do that it is in the best interest of your child.