<human>: We were at a small party last night with some friends, after the party was done, us and a few of the friends came back to my boyfriend's place and continued having fun. They left one by one until it was him, me and one of our friends (I'll call him Jack).

Let me explain some back info: I've known Jack for 18 months now, my boyfriend has known him for 4 years. They were buddies, but not close friends until around six months ago when both of us were getting closer to him. I've always had a slight crush on Jack (and I think him on me) and my boyfriend has always known about it. We talked about threesomes and we both have been interested. We looked through the people who would be good candidates for both of us, Jack was among them, but we never finalized a decision or plan.

Back to last night, I told my BF that this may be a good chance to try something with Jack. He agreed. So I flirted with him a little, made a move and the rest followed. It ended up being an amazing night for me, I really enjoyed it in every way, and from what I could tell, they both enjoyed it as well.

In the morning after we woke up the three of us talked about it, how it must remain our secret and there's no plan of repeating it until all of us have time to think about it. Everyone seemed in agreement, Jack left.

My BF however is acting weird. He says that he feels inadequate or incapable because I seemed to be enjoying it too much, that somehow he's incapable of satisfying me. I explained how that's not true and how amazing he is but it didn't seem to work no matter how hard I tried. And he's feeling a little insecure about his size, since Jack was a little larger (my BF isn't small, he's average salary sized).

How can I make him feel better about himself?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: BF and I had threesome with a friend. He's now feeling insecure and he's not confident in his sexual abilities.