A couple of friends of mine were organising a dinner at one of their places for our group to meet. I told my boyfriend that there might be an event for us to attend in the next week, so he could plan accordingly. Turns out the group decided later that no partners should come, so everyone could be comfortable to talk about problems and intimacies, as most of the boyfriends/girlfriends of the group are relatively new.
I told this to my boyfriend, but he didn't take it well, even though he wasn't going to attend anyway. He started asking if I had any secrets I was hiding, that he thought we didn't hide anything from each other. I told him that I had no secrets, but that some people of the group might not have been comfortable to talk about some subjects in front of him or another significant other, for lack of intimacy.
Some months later he still uses this as an excuse to not attend some events, saying that if I go alone I'll feel more comfortable in talking. I feel like he's not being reasonable, considering that I explained that the request to be a friends-only event was made by the host and not myself, and that it sounds reasonable not to feel automatically comfortable talking about private stuff on front of your friend's lovers.
I've been completely sincere, yet it doesn't make a difference. How do I clear this situation so that this card doesn't get played anymore?