Introduced my boyfriend to MFF. Over the weekend he crossed a boundary. We've talked it through, but I'm still a bit upset and not sure how to handle or move forward.

My bf is pretty vanilla, which I'm totally okay with because I absolutely love him. When we started dating a year ago we talked about sexual interests and such. He said he'd never had a threesome, and I asked if that's something he'd be interested in, as I've had a lot of fun anytime I've been involved as the 3rd. He said he'd always wanted to try it, but wasn't sure because he wasn't attracted to/didn't want to touch anyone but me. I told him I absolutely understand that and don't want him to try anything he's not comfortable with.

About a month ago it happened when we went camping with a few friends. One of my female friends (who I've hooked up with in the past) ended up hanging out in our tent with us after everyone else went to bed. When things started heating up, I told him I want him to only cum in me. They both happily agreed to that and we had a fantastic time. She came camping with us again the following weekend and again, everything went super well and we all had fun.

Over the weekend we went camping for a friend's birthday. I had a pretty shitty week with work and had a lot of anxiety going into the weekend. He agreed to be extra sensitive since I was feeling pretty on edge about a lot of things. We stay up drinking and chatting with friends until about 1am. I told him I was tired, but he could stay up and hang out if he wanted. He offered to walk me to bed, which was sweet, until he invited the previously mentioned friend to come with us.

We don't say much, and just start hooking up. Then he cums in her. I asked if he came and she immediately told him he better apologize. He said, "sorry, but what was I supposed to do, tell her to stop and get off me?" I got up and got out of the tent. Walked way out into the dark and found a nice rock to sit on and cried for 30 or so minutes, then went to bed and cried myself to sleep.

Is the boundary I set unreasonable? He had no problem sticking to it the past 2 times and vocalizing when he was going to cum so she and I could change places. He feels really shitty now and has said it'll just be us two from now on, but really I'm fine with bringing in others, as long as he communicates with me. I feel like he really violated my trust by not asking if that's what I wanted to do instead of going to bed, then by cumming in her when that goes against the only rule I asked for.

Am I out of line? I don't want this experience to shut that door forever, but I'm not sure how to feel better about it. Have any of you ever experienced something like this?