How do I deal with the fact that my gf had a lot of ual relationships before me?

The boyfriends were in her past. They will always be in the past. You cant hold this fact against her. Some find love within their first relationship. While others have 50 odd relationships till the right one comes along. Have faith in her or you will loose her. The past cannot be changed, but her love for you is probably greater than anything she had with anyone else. If you can't get over her past, maybe it is best you don't get married? Hope this helps!