Hi everyone, I (29f) recently got into a monogamous and exclusive relationship - we'll call her C (26f). Some background information:
When C first admitted that she wanted to date me (early February), she mentioned that there is just one thing that I might not be okay with - there is a man (lets call him T) she met when they were both teens and they started out as friends first and then eventually became romantic and sexual. He is polyamorous and she is open to polyamory or monogamy. He lives in a different state and they visit each other once a year. This year, he will be visiting her in May and staying at her place. She calls him one of her best friends and that just like any best friend, even in a relationship, she would want to visit him and she would want him to visit her. I told her that I am not going to control who she is friends with but that polyamory is not for me and if we were going to work out, it would need to be monogamous. We agreed to date each other, take it slow to test the waters and see if we wanted to pursue something more serious.
Mid February, I brought up my insecurities about T. She said they have been friends since they were 14 (I do not see how this is supposed to make me feel better about their relationship when the romantic and sexual boundaries have already been broken between them) and that they have good boundaries with one another. I brought up the fact that things happen when two people are alone and he may try to cross a boundary. She said if he were to cross a line, she would say something and/or kick him out and that she would do whatever to make me feel secure. After this discussion, I honestly felt good. I felt secure and trusted her wholly.
After about a month of seeing each other, C asked to be in an exclusive and monogamous relationship. She said that she would tell T that she just wanted to be friends and that he would need to sleep on the couch when he was visiting. I didn't have too many negative feelings about T sleeping on the couch, I trusted her.
This past week, I was telling C about an experience that happened recently with a previous crush of mine, who C had vocalized she was a little insecure about. The crush had laid her legs momentarily on me during a movie (this happened before me and C were exclusive). I didn't react to the crush's legs and I kind of just sat there and froze because I didn't know what to do. I wasn't exclusive with C, I don't actually know the crush's intention as women are usually touchy feely with other women, but I did know how C felt about her so i just chose to sit there and not react at all to the legs. C was extremely upset and jealous over this incident and said that she had wished I set some boundaries knowing how she felt about the crush. She said that due to issues in all of her previous relationships, she especially sensitive because her partners always ended up doing something with the other person she was insecure about. She wanted to feel reassured and secure and had asked that I (for the time being while she works on the insecurity and regains some trust) only hang out with the crush in a public space. I agreed as I obviously want her to feel secure in our relationship and I have no problem doing activities with crush in public spaces as we truly are just friends and have no romantic or sexual history.
After this entire incident, I started feeling a lot of resentment and anger about the fact that I have to be okay with T staying over at her house. I don't know anyone in a monogamous relationship who would be okay with this. To me , it doesn't matter that they are "best friends". The emotional and sexual barrier has been crossed and the relationship dynamic will never be the same. I know that if something is going to happen between them two, it will happen regardless but I would feel much more comfortable if T found somewhere else to stay during his visit. I am fine with them spending time together but spending the night even if he is on the couch makes me extremely uncomfortable.
Am I out of line for wanting this? I don't think I'm asking for too much. I want to set this boundary and obviously if she is not okay with asking him to stay somewhere else, I need to seriously re-think this relationship as it would be out of line with what I want and value. Is there a healthy way to communicate this to her without making it sound like I'm trying to enforce a rule? I'm not interested in toxic behavior or manipulation.
EDIT: She did tell T that we are exclusive so he is aware of the relationship. She has said before he and her have respectful boundaries but I don't know this guy so I'm wary