<human>: Give me the gist of the text in a nutshell

Soon after we started dating, a friend of mine told me he heard that she was 'fuck buddies' with our 'mutual co-worker', I assumed it was people talking shit and told her about it, the next day she told me that she'd gotten drunk and did hook up with the 'mutual co-worker', but it was a one time thing (besides it happened before we started dating).

She was sincere about the situation and I feel like I have no reason to be mad (and I am not), but it still bothers me that guy, the typical guy that sleeps around hooked up with my now-girlfriend. Our relationship has been going pretty well, I do not mention this at all, except for this everything else has been amazing, with the exception that we are temporarily in a Long Distance Relationship due me moving away for a few months, we continue to text pretty much all day long, Skype every night.

Even though I am sure that she does not talk to him anymore or has any interest, the guy still tries to talk to her, and some people at work know that they hooked up. It still just bothers me the fact that she slept with that guy, it bothers me that someone that in the future I may potentially want to get serious with, slept with a guy that I consider a scumbag.
<bot>: My girlfriend hooked up with a mutual co-worker before we started talking, even though she doesn't talk to him anymore it still bothers me that she did. How do I deal with this?