You have every right to be angry. You have been treated poorly. But lashing out at her does you no good. It might feel good now but shortly it will just feel empty. She should have not cheated. That was wrong. But direct your pain (for that is what rage is) at where it belongs - with your ex.
I'm sorry it ended this way. I'm sorry he was not capable right now of being a better person.
However, you have a child with him. That means he will be in your life in some way for the rest of your life. His cheating does not automatically make him a bad father. A bad partner yes, but he might still be a good father. Be angry at him. Rage at him here. Talk to friends about your feelings. But make sure to leave your child out of it. I realize she is an infant now and won't understand but get in the habit of not tearing him down in front of her.
You do not have the luxury of writing him off, as good as that might feel, as much as he might have earned that. You have to be the better person here and figure out how to co-parent with him. You do not have the luxury of being petty. Your child desperately needs you to be the adult and start working this out with him.
And do get treated for PPD. That is more important than ever now. I wish you the best.