I've been in what has become a serious relationship for 4 months now. It's been a very intense relationship, and we've been through a lot in a short period. Im a very skeptical person by nature, and it's taken a lot of work, but our relationship has solidified a lot, and I have put a lot of trust in her, and she has in me as well. The sex was a bit shaky at first, as we jumped into it a bit quick (for me anyway) but it has gotten very good, and very intense. We have sex prety much whenever we see each other - about 4 - 6 times a week.
The emotional aspect and trust we have in each other has grown a lot as well. It has been hard for both of us to find someone we can trust, but we both believe we have that in each other.
Now, here's the problem - she has a friend in another state she sees maybe once or twice a year. They have been friends for many years and although they considered a relationship at one point she has said repeatedly she wouldn't be able to stand him as a boyfriend and a relationship would never work with him. However, they have had a "no strings attached" sexual relationship on and off for several years. She is planning on seeing some family over Christmas, and knows she is going to see him when she goes home. This is the first time she will have seen him since we've been together, and she has said there's a good chance she will have sex with him. Not because of any dissatisfaction with me, but because they have always had a connection physically, and can both separate emotion from sex. She has explained it in length to me, because she wants to be honest and doesn't want to go behind my back. She knows I'm uncomfortable with it, and she doesn't want it to hurt or end our relationship if it happens.
What's hard is the fact that we have a very deep and emotional relationship. I have looked and tried to find some dishonesty on her part on the emotional side but I can't find any, so I know she is not faking her feelings for me.