Nothing stings you like bitch pain. I've been there (not married but multiple-year GF). While no on-line sancho was in the mix, I do think she was less than faithful. At any rate, if you loved this person as I have to assume you did, then the feeling won't go away just because you are separated. You have to accept that there is no escaping the pain. You must do two things. One, everything you do from now on you should always think about your kid. On a side note, though I don't wish you any additional pain, Necro is absolutely right about the paternity test. It isn't fair to anybody to live with false assumptions. Secondly, to get through this time the best thing you can do is to keep your family and friends close to you. Try to spend time with somebody every day, and though it sounds totally daytime tv, talk about it, seriously.
And for gods sake, don't come to video game forums for advice of this nature!