My boyfriend and I had our first threesome the other day, and while it was fun, there was a huge part that almost derailed the whole night.

We were in bed, and I was trying to ride the third guy. He was...a little to big for me, so I was trying to stretch myself and slowly take him in. My boyfriend started fingering him at the same time, and apparently both of us were a bit overwhelming, but he especially liked what my boyfriend was doing.

I didn't know what to do, so I got off, and my boyfriend and him started to go at it and finish within a few minutes while I sat next to them. It was hot, but such a shot to my confidence, I lost my mood quickly. They both finished and looked exhausted, and while they asked if they could help, I felt so small, and unlikely to get my boner back, that I said I was fine in the moment.

Fortunately, the rest of the night was good. It was filled with cuddling and hanging out, and he showed us some cool homemade cocktails and drinks (he is also a good friend of ours).

I've told my boyfriend about it later, and he said they can draw better boundaries (EDIT: He also said he felt bad, and was very sorry), but I don't feel very confident right now.

This threesome was a first for everyone, FWIW.

Advice from anyone?