Yeah, I agree it would be good to find out.
If you're still angry and upset maybe write the things down, journalling can help.. Then decide what you want to talk to them about.
If you live together possible problems could be related to that: food in the fridge, who ate what, who did dishes when, who
used dishes/food utensils and kitchen when, or household chores, or bathroom/flat hygiene (if you're too into clean stuff or don't clean enough), visitors or no visitors, noises from your room when your bf visits (or they might just feel 'shut out' and ignored if the two of you spent lots of time together cooking meals etc - happened to someone I know!! There was a terrible rift at the flat, with noses upturned etc.) Are the others single or 'coupled up' too?
Maybe one of them fell in love with you or felt 'misled' (some of my roommates could do that to people)...?
Maybe your laptop/PC is too loud when being charged or used, or you use it at inappropriate times when others want to sleep? Maybe your waking/active hours are mismatched? Or you (or your bf) snore? Or your clothes smell of cigarettes (or iffier stuff) when you return from partying? Or you cook bad-smelling food (to them) or there are bad smells from other things.. Or you don't like them smoking (or growing) pot... (?!) (Then move out asap!

) Things worth checking out... (Others may be too embarassed to tell you if you don't ask and thus sort of give permission to speak..)
If things were not stated ahead, the problem can be unclear boundaries: people just expected you to be a certain way, while never saying anything about it or just being vague..
Or people could get upset over a certain expression or turn of face (which may or may not have had nothing to do with them!), especially if they were there ahead of you and expect some sort of 'seniority' and privileges or even your 'gratitude'? (If they helped you get the flat?)
On the other hand, maybe they just want to get another friend of theirs into the flat.. Or at least one of them does and may have stated partial truths or untruths to the others.. It's vaguely possible, but still might be worth checking.. Or there may have been total misunderstandings.. (eg someone heard you say or do something and totally misunderstood?)
Maybe the best way to go about it would be to 'assume innocence' and ask, 'Hey guys, it seems there may have been a misunderstanding? Can you guys tell me what this is all about? Is anyone insulted over something I did or said?' (Maybe it's best to ask the nicest person in the flat privately? And then ask others privately, one by one, and see what they say?) If you ever took anyone's food or 'forgot' to clean anything or nagged anyone to clean anything, you could ask if this is about that..? (Even if it's not, they might tell you easier what it's truly about..)
You can even get them beer for 'the last time you're together' or something like that?
Or ask someone that's vaguely related to them but not so much part of the clique, eg a mutual acquaintance/friend? (They may find out easier than you.)
You're lucky you still have bf. It would be good to work on getting new friends yeah, both iRL and online.. Where did you meet this set of friends - online or in RL?