<human>: Can you give me the gist of the text in a nutshell?

Me 23F with my 24M boyfriend of 5 years, he wants to go to this 21st house party, of one of his brother's friends. We don't really know him that well, his brother just said "oh you guys could come".

 I'm not interested because I don't know anyone there, and they are a bit younger, and I find them rather annoying. BF really wants to go, I don't know why I care so much. The fact that he wants to go makes me upset, and that he's going even though he knows I care makes it worse. I know it's completely irrational, but I don't want to ever see him again because I feel like "it will teach him a lesson". 

What lesson am I trying to "teach" him? Why the F*** do I care so much?
<bot>: BF wants to go to some guys house party, but I'm not even slightly interested. Is it irrational for me to care that he's going without me?