Why does my boyfriend looks like he has more fun when i'm not around?

Well, my boyfriend (25m) and i (23f) have been together for 1.5 years
Yesterday night we went out with our respective friend groups, since we live in a small town both of our groups were near, so at some point in the night i got up and went to say hi, all of his friends greeted me and i noticed that there were a few of his female friends with them (He told me none of the girlfriends were going so that why i wouldn't be comfortable there since i would get bored, and i agree with it, that was true, but there were girls there so i wouldn't have been so bored). Well, they were paying for their dinner so i didn't stay long, since he was busy calculating the bill. Later he told me he felt bad because he didn't pay much attention to him and came to say hi to my friends, i told him it didn't matter since it wasn't on purpose, even though i was kinda hurt by it, but i brushed it off and continued with the night with my friends
Later, some of my friends went home since they had to work in the morning, and only three of us were left. My boyfriend texted me saying that he was kinda bored, so i told him to come with us, It was a celebration for our town, so there was a free concert where i was.
So, he came, and he was just standing there, even though i have seen him sing with his friends, dancing and having fun. I didn't think much of it since his mood was a bit low, so i tried my best with singing to him and dancing and trying to make him have fun.
It didn't work, and my friends left us alone, so i tried harder, but he was just standing there.
His friends came to the concert, but they went to another spot further from the stage and i could see my boyfriend looking at them constantly, so i asked if he wanted to go with them a couple of times, he said no with a sad face, the third time i told him i was going home, and he said okay and left with a smile on his face, and i had to go home alone.
Why do i feel that my boyfriend has more fun when i'm not around?
Updates
1 y
Today he went out with his friends even when he knows i'm upset. And my friends don't have any plan of going out tonight so i'm sitting at home alone.
Updates
1 y
He told me the same thing "None of the gfs are coming tonight". But i just saw a story of one of his friends gfs and she is out with them.
Why does my boyfriend looks like he has more fun when i'm not around?
Post Opinion