My wife is pregnant with another man's child

I think you definitely should divorce your wife. She had an affair and then she wants to keep the child. AND the guy wants to still be part of the thing. Don't be come the victim here. Get out and get them both out of your life. You deserve better than this. Get help straight after. The links that people posted here are great, so just do it. You have nothing to be ashamed about, your wife and her affair does.