We all experience periods of life when we feel down. Has to be or we'd not appreciate the up periods. Worth remembering that nothing stays the say. down today, back on the up & up sometime in the future.
So the party wasn't as wonderful as you'd have liked. That's life, one party really isn't a big thing. Honest.
Your boyfriend got jealous and you say he had no reason to. Well you can't control others feelings. Talk to him and explain,. If he can't accept you have a close family friend then that's his problem, not yours. Maybe he isn't the one for you after all then. at least not yet, not until he's grown up a bit. (That said I'm mindful of the fact we only have one side of the story.) But try to talk it out with him first. And if you think you've done all the attempts at talking you can take, well maybe time to move on.
Breaking up is depressing, but it doesn't stay that way, and it's not as depressing as staying for ages in a relationship that makes you unhappy.