Trust me bro I feel the same way, but I'm to my limit. This is the second time she has slept with a co worker within the last 2 years, hell the last time was still fresh.. And the crazy part abt it, she came from a broken home.. Never knew her father so you would think she would want better.
Man, first off, I'm really sorry to hear about all of this. What a messed up situation.
Now, my 2 cents: get a lawyer immediately. You NEED to protect yourself here. Your house, your child, half of everything you make... all of this is going to be on the table for her in a divorce situation. I'd limit all interaction with her, too, as hard as it might be. If she agitates you into raising your voice, she'll claim emotional abuse, especially if she can get your neighbors to say they heard you yelling at her.
You need to be really careful with everything you do. But definitely talk to a lawyer ASAP. It's going to cost you, but if you guys do end up going through a divorce a good lawyer can limit your losses and ensure you get as much custody of your child that you want to/can have.
I really hope you guys can work things out, but from my experience (my dad, my aunt, and other family members & friends): a cheater's gonna cheat.