Move on! We know it might not be what you want to hear but it's the best advice. Not only did he sleep with another girl, but he obviously didn't use protection, putting you in danger of contracting STDs. She will be in his life forever because he is bound to her by their child! If he does the right thing in this situation, which will be supporting this girl and their unborn baby, he will have way more responsibility on his hands and will not have the time or energy to put as much into your relationship.Cheating is a terrible betrayal and if couples survive it, then they need to work at their relationship. He won't be able to give you this energy because he'll now have to consider another person. It is best to move on and find someone who will respect you and definitely not consider hooking up with another person. Good luck!