My wife is pregnant with another man's child

I think that you should file for a divorce, because not only has she committed adultery, but the father of the child wants to be a part of its life. This will be difficult overtime because it means you're probably going to have to accept the fact that your wife will be contacting this man and having him be a part of her life too. She may sleep with him again (if she can do it once, she can do it again), and you'll have to go through the betrayal once more. She made the decision to cheat, so she has to deal with the consequences. I could never imagine having to go through such a thing. Stay strong and seek help. You will get through this.