@Open Eyes I think all anyone can do is share their perspective, which will always be colored by their own experience. You've shared what stands out to you, and there is absolutely nothing wrong with that. The concern I have is when one person or another tries to establish that they are right. None of us can be right. It's not our life, we're not there, we have no clue what's really going on. All we can do is share from our own experience how we have dealt with similar situations.

What's there for me in this is that regardless of the reason, the OP is uncomfortable being with a woman who has more sexual experience than he does and has lived a different lifestyle than him. He seems to have trust issues as well as insecurity about the relationship. He either needs to deal with these or end the relationship. It's not fair the GF either if he is constantly untrusting of her for no reason. And that's not a healthy relationship for either of them.

I also hope the OP returns to give us some more background.