Reasons being: 1) I can't win with my parents. 2) I always end up disappointing my BF

Stop acting like you have no agency here. You are allowing your parents to call the shots. Even worse, you're forcing your boyfriend to be the one to cancel the trip because you don't even have the guts to do that, so you waffle and pretend you can't decide until he makes the decision for you. You're an adult. Nobody can ruin a trip for you except you. You can win with your parents by refusing to cave to their manipulative bullshit. You can stop disappointing your bf by growing a spine. You aren't the victim here.

It's long past time to grow up. This is pretend helplessness. You had a choice here, and you made it. You decided to let your parents control you (pretty rich of your mom to claim your bf has you in his pocket when clearly she's the one who does).

If you don't start making your boyfriend a priority, he's going to get fed up and dump you. Or at least if he had any self-respect, that's what he should do. You haven't seen him since October and you allowed your parents to call the shots without discussing it with him. That's pretty shitty.

How do you create boundaries? Before you even arrive at your parents, you tell them you are leaving on X day and that it's not negotiable. If they throw a fit, you don't come to Christmas.

You're letting your parents control your life and then throwing up your hands pretending you're helpless when you're not. You're so afraid of conflict that you don't tell them when you're leaving til the last minute and then act surprised when they're upset (you KNEW they were gonna be upset for the get go, what's the difference if you told them earlier?). Then, even worse, you pretend you're so conflicted and undecided that you're paralyzed with indecision, forcing your boyfriend to make the call to cancel the trip so you don't have to be the "bad guy." Stop it.