I (23F) and him (23M). Experienced one of his wants together. That I, for the longest time, hesitated due to the fears of what could happen in the scenario. I always would like to be the third wheel, but when it came to being the one in the relationship, it wasn't much of a want. It's just something to cross off the bucket list if i had drank too much. I'm not sure if I can say it, but I just need to get this off my chest. We have dated for 7 years, married only 1 year. Now, to be perfectly clear, it was a consensual, mutual between the three of us. My only downfall to the whole part about enjoying it all is that One, we never really set boundaries altogether before doing it or putting down rules. She's a new friend I met but instantly connected with, she also is married.

Well, we at least had to be going for about an hour and her+I finished, he hadn't but I was satisfied at that point. The continued at it for another two hours basically whether or not I was in the room.. Mind you, my S/O always said he'd rather it be an effort together, even when I straight up told him the past, I'd give him a freebie to go fuck another girl with out me. He always insisted he'd rather share it with me. Some details that will make it seem worse is that she wasn't on birth control like how I am, and we had no condoms.. I know she wouldn't have his kid even if pre-cum caused her to get pregnant. Fast forward 4 hours later, he still convinces me to cuddle her and get in bed even tho I wasn't tired, he had to go to work in an hour. I leave the room because I wanted him to be considerate about how I felt, I go back in the room after 5 minutes. They are fucking again, at that point the experience for me became really unpleasant and I feel hurt, devastated. I just don't believe that couples should have threesomes unless they have rules and boundaries set up. Or unless you are completely open to having an open relationship. 

I handled it well and fun in the beginning but something clicked in me after I was no longer apart of it and it just continued. Am I the asshole for feeling the way I do?

-Edit- We have in the past multiple times discussed on both sides what we wanted from each other if we did this together. So clearly, it should have just been rediscussed right before the actions were taken. I have said my rules and boundaries a lot in the past, every time we have ever had the conversation if we were to act upon it. Also, there's another side of this story that's not my business to discuss. I'm only saying mine. The freebie was meant for me not to be around for it, but he refused to do anything unless I was involved. Also, that "freebie" expired before we got married. The whole point of it was so I didn't have to emotionally involve or present and feel the way I do now.