Figuring out the ropes
So I've been looking for advice on my relationship for a while but none of my friends can really provide any good insight so I"m hoping ya'll can.
My boyfriend and I have been together for just about 5 years and have a great relationship and will be getting married when I'm finish with medical school. I brought up the idea of an open relationship several years ago and after a long conversation, we both decided it was something we wanted to try. Since them, I've had a couple of flings and he had until very recently only had 1 one-night stand. We just moved to a new state (he moved for me) and I lost all of my potential dates in the move. I'm now incredibly busy (med school tends to be that way) and haven't had any real desire to find anybody else. We have slightly different rules than what may be the norm. I don't mind if he bring people to our apartment as long as he doesn't ask me to leave for it. He has to have sex with me before he can sleep with another girl. No staying the night and no getting attached. We're interested in the open relationship for the experinece of sleeping with other people not true poly-amory.
The drama in our relationship has come of late due mainly to this one girl he's been seeing. She's a co-worker of his and they started out texting quite frequently, sending pictures and whatnot but I wasn't aware of it. He mentioned he was interested in a girl at work but hadn't mentioned he was texting her so much. This started in Dec and towards the end of the month, I found all of these texts on his phone and at the time he was asleep. I felt really betrayed that he wouldn't have told me about this girl if it was getting so intense and we have the type of relationship where I want to know everything (I get my rocks off to it a bit). We talked about it and I felt reassured that he wasn't trying to hide anything and just hadn't thought it was a big deal. For our relationship thus far, I've been the one out with other people so it was new territory for me and I know I was being kind of silly.
Since then, they've continued to talk and have made plans to get together while I'm gone but every single time they make plans, she comes up with some excuse (ranging from car breaking down to "just not in the mood") and it's been incredibly frustrating for me because I feel like she's just been playing with him and I"m protective. This has been going on on a weekly basis and sometimes multiple times a week and they still hadn't hooked up. I'm out of town for the week and so it seemed the perfect opportunity for them to get together and yet, more excuses came up. Que to today, where I spent the afternoon talking to my boyfriend about this situation and we both came to the conclusion that she was just toying with him and it was time to end things. Then, this evening, she shows up and they have sex. My reaction was less than pleasent. For whatever reason, this woman bothers me more than any of his other flings have (he also within the past week had a friend come down and they hooked up and I was fine) and we got into an arguement about whether or not things should end with her.
My issue is that I don't trust her. I think she has alterior motives and enjoys screwing with his mind. He claims she doesnt and the fact that she put out is evidence enough of this. I don't want to tell him he can't see her. I don't feel its fair for me to say that and aside from this one girl, our open relationship has been working great and I can't help but think part of my discomfort is because I'm not actively pursing anyone else. I guess I just wanted opinions from other people who are going through this that might be of some help.