My girlfriend and I have been going out for six months and are deeply in love. She is the most honest person I have ever met and has openly brought up her past with me. We both volunteer in our free time and have the same volunteer manager; who we are both good friends with. However she told me that about a year ago, long before we started going out, our manager had just been divorced and he asked her out. They went out for less than a month and then he ended it (it was clearly a rebound but she didn't see it as yet another toxic relationship). She also told me that they had slept together - and that is where the problem lies. She has had plenty of sexual partners in the past and I haven't had a problem with any of them - but that may be because I didn't know any of them personally. Now all I can think about is the two of them doing it; and it's driving me crazy. She says that they will never be more than friends in the future; and I believe her, but at the same time I can't get the idea of them two doing it out of my head. I really don't want the relationship to end; but at the same time, I don't see how it can continue when all I can think about is the two of them doing it. Does anyone have any suggestions?