My wife is pregnant with another man's child

This is Sick! that man wants to be a part of the childs life WTF. Get Divorced and come out of this s***. bz if you dont come out you will suffer it mentally forever and you would never ever can stay happy you might mess your life in such situations and even if you want to carry this on ahead then its yours choice bz this is the time to jump off from this before it becomes late to come out. Also you said that you have started feeling depressed so you can understand if this is current state then what can you expect in future So once again get divorsed and stay alone for some time and also consult an counseller for how you are feeling right now. Best of luck