Too laid back for me too. I have to plan everything in case my anxiety rears its head and I needneedneed an exit strategy. It's frustrating to no end, but it looks like something I'm just going to have to deal with in the end.
I think you are right - you will need to learn to deal with the different social norms of your BF's group of friends.
But, on the bright side, you do have time to plan for different scenarios. For example, you and your BF could take separate cars to a party, so that if you're getting run down, you can just go whenever you want, and let him stay. Or, you can talk through ground rules for living together--like, no spontaneous gatherings of more than 2 people at your house, or you agree that you might stay in the bedroom rather than socialize with people if they're not your friends, or something like that.
Back in the day, when I had a roommate, we didn't have the best communication, I admit. I once offended her and a group of her friends when they wanted to come over to our apartment "right now." She was like, "Hey, Joe and some people want to come over now, is that cool?" expecting me to just say yes immediately. And instead I was like, "How many people? How long will they be here? What will you guys be doing?" I eventually said yes, but only after she answered those questions; and the questions, plus the delay in saying yes, offended them so much that they felt unwelcome, and ended up not coming, and she was peeved at me.
Okay, obviously I feel I was in the right
but to be honest it was probably more a matter of different styles, and this particular issue just hadn't come up before. I'm just not a spontaneous person, nor do I like having lots of near-strangers in my space for an indeterminate length of time--I imagine I would be trying to do my own thing in my room, and maybe they would be loud, and maybe I would feel like I couldn't use the rest of the apartment until they left, etc.. And clearly she felt differently--these were her friends, she didn't think they would be out of line or doing anything weird, I could/should join them and get to know them better, I shouldn't feel inhibited around them, and this was her place too and she ought to be able to have friends over whenever she wanted.
Nowadays, if I was sharing space with someone, early on I would say, "Let's set some ground rules for friends coming over. How much notice they need to give, size of the group, how long they stay, activities in our shared space, etc.." Then when the question arose for real, we would already have a framework to use.