If it was emotional fidelity, I might consider starting therapy. The reason is that emotional loyalty may mean an issue that needs to be raised and talked about. To understand why that partner is detaching emotionally and how to fix it. With a counselor, there may be hope to fix the relationship and figure out how to communicate better on an emotional level since that was the cause of the fidelity. If it were the other two options: physical and open, I would leave them. If they act on their sexual desires with someone else while in a relationship with me, that tells me how much they don't value the relationship and I'm unable to give them the sexual satisfaction they need to move forward. It can be difficult to maintain mutual sexual gratification, but with clear communication and understanding you can make it work without relationships and fidelity. I wouldn't want to be in an open relationship because I wouldn't want to risk our relationship falling apart due to having sex with other people. I can't imagine being with someone else exclusively for sexual acts and going home with my partner while being all okay. My partner and I must fully commit to our partnership in all aspects. If my partner wanted to have that type of relationship, I would leave