<human>: Can you succinctly summarize the text in 1-3 sentences?

We've been together for about 5-6 months. 

I've looked around for similair feeligns (which is hard since I'm not sure how to adress nor describe the problem) without much success. 

I'm not worried about my gf cheating on me. She is the last person to cheat, and especially with me - I am 100% certain on this.

The thing thats bothering me is simply put her with another man. 

For example, we were playing a drinking game called I have never and the question was: I have never had sex outside (i.e have you had sex outside?). She had. That thought really puts me down, changes my mood entirely. Furthermore, I get pissed and annoyed at myself for thinking like this. I'm not worried that would happen again while with me, it's just the thought that fucks me up.

In my last serious relationship i got cheated on atleast 2 times. Been having some trust issues (is this trust issues?) since. 

How do I tackle this? She is really understanding which is nice, but I still want to stop feeling like this. Drives me crazy. That image of her outside with another dude outside is stuck in my head.
<bot>: Not worried about her cheating. It's just the thought of her actually having sex with anyone else (before me or after me idc) which drives me insane. Ex probably caused this. What do?