Whatever you decide is up to you, just make sure its based on your happiness, safety, and wellbeing, and not because its easier or you feel pressured.
Think about whether you can live with this, or whether you can't.. Think about the chances of it happening again.. Think about the lack of respect to you, and to his and your child
Also think of the fact that he has carelessly exposed both you and baby to life threatening diseases through his selfishness.. remember that he's been "caught" twice, and think of the men in the brothel, bringing god knows what home to their families.. Think about whether he'd be sorry at all right now if you hadn't found out, would he? Or would he be sitting on the couch right now happily plotting the next time? -remember he's only shown remorse once he's been caught, then went off and did it again..
Life can be tough sometimes but if you look out for yourself and surround yourself with the right people, plan ahead and get your priorities right, you can rise above anything, then look back laughing later..
I agree counselling would be ideal, these things cause teh same kind of PTS symptoms as losing a family member/loved one or any other kind of emotional trauma, which is probably why you are thinking such negative things right now..
Best of luck to you, you didnt deserve this, and you don't deserve it any longer!