getting even

why does he have to get even when he thinks i'm "jerking him around," as he says? he's trying to make me feel what he feels.
i'm so outraged, but i have to stay calm. is it ok to have an escape on the back burner? i find comfort in knowing that if i can't take it i can move. but i would never tell him. i just don't know how strong i can be sometimes.
the issue was we were invited to our band member's birthday dinner (male) saturday. he (SO) isn't gonna go because he was planning to watch football payoffs. he said he could handle me going. i wanted to go, but i thought i couldn't afford it, so i said i wasn't going. then i found out it was inexpensive, so i changed my mind. my SO isn't comfortable with me going because the band member is a man. even though it's not a romantic one-on-one situation, it's a birthday dinner party at a restaurant. ok. this came out tonight, so i agreed not to go. i'm frustrated, but it isn't the end of the world. we have a fight about it, i try to make him understand that i want him to recognize how often i adapt to meet his emotional needs (that's not supposed to sound sarcastic, hope it doesn't, event though i feel very capable of sarcasm right now). he says he feels ashamed of how he feels, and also says that i jerked him around by changing my mind, because he felt undisclosed relief when i said i wasn't going. he said i should have known intuitively. well, i did know intuitively, but i also asked him how he felt about it beforehand, and he said he could handle it. and not just offhandedly. implored, checked in, asked again. i took his response as hope for me. can i be hopeful, even if i know it to be ridiculous? i need it. and it's not like i'm going out alone with an ex. to me it is a safe situation. to him it is not. i respect that, even if it is begrudgingly.
arguing ensues, but it seems like there is a glimmer at the end of the tunnel. then he tells me he is going to go hang out with a girl he's dated in the past that used to have a huge crush on him. i am to go to the dinner, he is going to go out to a show with her, and i am not invited. why would he do this? so i can see how he feels, he says. he can't understand how wrong that it. he says i hurt him. i can't make him believe it wasn't intentional. and i already said i wasn't going to the dinner because of his feelings! and does he think i would go after what trouble the possibility caused? he wants to know why this hurts me. i want to know why i don't i leave, but i don't say this.
i would never go out alone with a guy on a saturday night drinking at a bar and tell him he's not invited. no brainer, i said! but this isn't about how witty i am, or how powerful my retorts. he.can.not.see.it. he said he's canceled the plans. so now we'll have a glum saturday evening arguing or just staring at each other, maybe watching a movie at home.
i'm trying to recall how happy i was a week ago. i need to hang on to the hope. i'm on a course of some kind, a path that will take me to a deciding point, or to help, or to more hope, or to me on anti-anxiety meds (bad joke?). he keeps telling me he doesn't have bpd. maybe he doesn't, but whatever it is, it's pretty effing hard to handle sometimes. 
why would he do something like that, though? and i think he was planning it an hour before he told me he wasn't comfortable, when i agreed not to go. i saw him texting someone, but he wouldn't tell me when he first contacted her. refused. "i don't have to answer that." asks me why i don't trust him. why i don't give him the same respect. how do i set boundaries when he does things like this to intentionally hurt me? i really want to bawl, but he's in bed in the other room, the apartment is small, the walls are thin, and i work in 8 hours. i don't have time for this? do i?