This happened during a 2 month break that occurred due to me being out of the country during that time.
To expand upon this, we met each other 2 months before I left and were pretty crazy about each other, however sadly thought it would be best to not stay together due to the uncertainty of when I would come back and if things could work out long term for us. It was a strange situation though, as we (very stupidly it turns out as it has resulted in much hurt and misunderstanding) continued to speak basically as if we were still together as our feelings had not changed for each other, it was merely physical proximity keeping us apart.
When I returned, we got back together almost instantly and it was bliss until about 2 weeks later when she told me that she had slept with someone else while I was away. It was a one night thing with a random friend of a friend at a party that she very much regrets and a big part of it was to try and get over me since she did not have the same optimism about our future as I did. I personally did not do anything with anyone else while we were apart since I knew I did not want to ruin my chances of getting back with her, and based on the way that we were speaking and how we still felt about each other I falsely assumed that she was not doing anything with anyone else.
I try not blame her for it, as I am aware of the fact that exclusivity is not something that can be assumed, and in some way blame myself for not making things clearer. I wish she had told me when it had happened so that I would not feel mislead and would have known where we had stood, but she says that she assumed that I was getting up to similar things as her and did not want to know what I was doing in that regard.
It is just a horrible feeling that someone else was with her in that way between us having a break and getting back together. How can I not view our relationship as tainted by this guy in some way? Stuff that happened before we met does not bother me in the slightest but this really does due to when it occurred, and I would do anything to rid myself of these feelings.
I suppose it comes down to whether it is something that I can live and deal with or not, and to be honest in most situations I would realistically battle to get over it and probably tell her that it is best that we move on, but I really love her and want to make this work. Would appreciate some insight and advice on how to not let this plague me and the relationship