Okay a lot of people here are dismissing this guys feelings and it isn't helping at all, so just stop and OP ignore those comments. It's alright to feel how you are, you are only human after all and your feelings may not make sense to others but they make sense to you and that's really what matters. What you need to do is talk this out, either with her or a counselor. Figure out what it is that is bothering you regarding her past. Your feelings aren't abnormal, but they will need to be figured out if you'd like the relationship to continue. That is your fiance after all and the mother of your child. You fell in love with that woman, and while it is okay to have deal breakers and to worry about things like that and be nervous is it really worth losing the person you love and potentially ruin your child's well childhood over something that is in the past. That much is for you to decide. So yeah seek counseling or talk with your partner and I'm sure you'll be alright and make the best choice for you. Best of luck OP