<human>: Hello there fellow redditors!

My gf and I have been in a relationship for almost a year now, and we are a very happy couple. She is my first girlfriend and my first 'experience'.

She has had multiple boyfriends, among who a guy that just used her for sex.

She has done some stupid things. Before we had a relationship, she used to hit on a lot of guys. She had sex with one of my friends. I didn't really care about that tbh, but I told her that I did care. One week later, we were in a relationship and I lost my V-card the same week.

Now here's the problem: I created a problem of my own, where I keep thinking of my 'friend' having sex with her.
You'd think this isn't such a big problem, but it occurs when we have sex as well. 

I can't talk to this friend anymore without thinking about it.

We have been talking a lot about this problem, and we always end up with her crying in regret about the mistakes she made. She calls herself a 'slut' and I feel bad about her feeling bad.

I know she's on Reddit as well, but I just want external advice, because we can't sort it out together.

Do you know how I can get over this? I try not to think about it. I know it's the past, but it's still floating around in my head.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: GF had sex with several guys before our relationship, including a friend of mine. I keep thinking about him having sex with her, even when I'm having sex with her. How to get over this?