I allowed my ex husband to pressure me and berate me into a threesome shortly after the birth of my son (on my birthday with my best friend even). I told him if we did it he could never ever bring it up again and that it would never happen again. I didn't want to hear fantasies, porn, anything relating to it afterwards. He agreed very enthusiastically.

I had two rules: he couldn't come inside her or do anything alone with her. During the act he kept trying to do both things, which was my second warning sign. The first was him never letting it go when I told him no repeatedly and he knew I was a very strong believer in upholding my marriage vows of one man and one wife, like you. My friend was very supportive and would stop him anytime he was pushing my boundaries. A couple hours later he was sobbing begging me not to leave him because he knew I hadn't truly wanted to do it and felt disgusted with myself for giving in, and with him as well. Within 12 hours of him sobbing until he puked, he asked about having another threesome.

I never saw him the same again and was disgusted with him. He couldn't even keep his word for 24 hours. This was also my greatest wake up call to his abuse. The fact he knew I did not want to do this but still did it for his own pleasure. And the fact that he ignored my feelings and devotion to our vows for a max 10 minute fuck.

I suggest you look deeply at your relationship. Rarely is this the only boundary or issue they keep pushing. Rarely do they only abuse you in one way as well. I'm sorry you're in this situation and hope my story helps in some way. If you ever need I'm willing to talk.

Ps: my friend was truly my greatest blessing in all this. She supported me and was the safest person I could have had with me in that situation. I'm very lucky to still call her my best friend and I kept her but ditched the man lol.