E.M.
I'm so sorry you are going throuhg this, it sucks, plain and simple.
I admire you for trying to forgive and forget, but that is going to be very difficult. I would be upset (more like madder than hell) that he cheated, but more that he cheated without using protection. I recommend you get tested for any and all types of STDs. It will be scary, but you deserve to know if he gave you something. If this woman told him he didn't need to use protection, God only knows who else she told that to. You need to protect yourself. Also, go to a lawyer and see what you can do about separating your assests. If this is his child, he will need to pay child support. The courts will take into consideration what he has and makes. Regardless if you remain married or not, you need to protect yourself and children. You need to know you can still afford to live the life you made for yourself and family. If he needs to get a 2nd job to pay any bills outside if your family, he'll have to do it. If he really wants to be forgiven, he will not be upset about this.
It's good to know you have strong supprt from your family and his, but remind them not to talk poorly about him in front of your kids. He cheated on your family, but they don't need to know that until they're older and can make their own decisions.
Good luck with all of this, sounds like you need to call up your girlfriends and go out for a drink, you deserve it!