I suggest that you arrange to have a conversation in a non sexual setting and first express your understanding of her view, then the angst/difficulty this situation causes you, and only then ask for possible solutions or a comfortable middle ground. Your post suggests she sees only one person; maybe finding a second who wouldn't mind you present.
I broke up with the couple that I enjoyed most in over 20 years in this lifestyle. We were exclusive over two years. He and I were both NCAA basketball fanatics (him Indiana, me UNC) and shooting pool. He worked nights and if I spent the night most times I got there before he left.
He wanted to watch once, and I had NO problem with it, but she was resolute it would never happen. He slowly increased letting me know....and he was an assistant chief of police in a suburban community. The more he asked the more I thought of being a Black man 'caught' in his wife's bed in the ultra conservative South....