<human>: Me and my girlfriend met at uni in first year and have been dating for 2 years. 15 months ago she quit uni and moved home (about 100 miles away) so we've been doing the whole long distance thing with me finding a job there to move in after i've graduated. 

About 7 months ago we split up. The details of this aren't paricularly significant but it was her decision to end it. We were apart for about 2 months after which we got back together and are where we are today. During this period of separation we both had sexual experiences with other people, "We were on a break!!". 
Things had been going great since we've been back together, it was exactly how it was before we broke up. However, last week she got really upset and told me that the whole time we've been back together she can't stop thinking about the other girl I slept with. She says every time we kiss, cuddle or have sex she is reminded that I have been intimate with someone else.
We had a huge argument about it - mainly me saying that I managed to get over the fact she had also been with someone else. I told her that I hate the fact she slept with someone else, but there's no point dwelling on the past and I just focus on how much I love her and the fact that I know she wants to be with me. She tells me she's tried and tried to forget and move on but she can't do it. 
This is really damaging our relationship. She tells me I can't do anything to help and is refusing to seek any help in the form of counselling. What can I do to help my girlfriend get over this so we can be happy again?

Summarize the given text in a few sentences.
<bot>: My girlfriend is struggling to get over the fact that I slept with someone else during a break we had in our relationship (she did the same).