<human>: Can you provide a brief overview of the text?

Hey, throwaway because she knows my Reddit username.

So, to give some background. I've been dating this absolutely lovely girl for almost half a year. The first time I was at her place we watched a movie and talked about previous relationships, I don't remember what the context was but I vividly remember her saying "cheating is something that just happens". 

I should have asked her what she meant by that but I didn't. I myself have quite strong feelings about cheating and I get really angry just thinking that people actually betray and cheat on their partners.

Two weeks ago we agreed on being exclusive. 

Here's the issue, I've been on a vacation since Thursday, will get back on Tuesday again. Already on Friday I've started to have quite unrational thoughts that she would cheat on me. They had a company party that evening and I know she likes a guy at their company, and yesterday evening she was at a party as well. She told me on Facebook that she went home early on Friday night and she usually check Facebook early in the morning, this time she wasn't online before 4pm the next day.

I'm getting angry at myself for even thinking that she might cheat and for not trusting her and also that I bother caring about when she's online on facebook. Because it's all in my head. I would consider myself confident in many ways, I think I look good, I'm a fun guy and I know we are a great match, and she said so herself, I try to be honest with myself so I realise that this issue I'm having is due to some kind of confidence issues on my part.

I think (and hope) all of this would be solved by just talking to her about what she said about cheating. Getting her point of view and also expressing what I think about it.
How do I approach this to not get her to think that what she said is all I've been thinking about?
<bot>: I've been having unreasonable thoughts that the girl I've been seeing exclusively is cheating based on a single sentence she said. I need help with my personal issues