In a perfect world, sex would only exist after marriage. Unfortunately, we are curious creatures and feel the need to explore others both sexually, mentally, and even sometimes spiritually. Often times these escapades teach us a lot about ourselves, our wants/desires and we also learn a lot from other people. It is understandable that you may have trouble accepting the fact that your girlfriend and the mother to your child had an intimate past with other men, but you have to consider your own past as well. Would either of you have come together if your past didn't shape you into the people you are today? Would you have created such a beautiful child? I'm sure she doesn't even give much thought to her past encounters as you are doing now. If you want to keep and protect the family that you have now, you have to let the past be the past, otherwise you're ruining the potential for a great future.