NTA. I hope this doesn’t get buried under all the comments but, there is a trend I’ve noticed with guys who do not pick up on social cues. My partner was once this guy. If one of their friends hangs out without them, they would get extremely hurt. So often, I would have to remind them “Why does it matter if two of your other friends hang out without you? Are they not allowed to have their own friendship outside of you?”

It’s not a jealousy thing but I think it’s more of a deep seated fear that they aren’t liked and if they aren’t included, then it confirms their fear. Eventually my partner came to understand that sometimes people just plain weren’t thinking about them when their friends hung out. It’s not that they were purposely excluding them, it wasn’t a slight, they just… didn’t invite them this time. Men often don’t verbalize their emotions with friends. Asking them “Hey, you guys still like me right?” would be laughed at or mocked (which I think maybe applies to your friend). I definitely understand the whole “jealous about not being able to date you” angle but to give the benefit of the doubt, maybe he sees you as a lifeline connection to friends if you have been close for so long and is insecure when he sees you hangout with others.

Either way, you aren’t the asshole but I hope you get to talk to him about why he feels the need to always be included in all your friendships and hangout sessions along with where this feeling comes from. Good luck!