aita for not wanting my best friend to be friends with my bf?

[LONG BUT I REALLY NEED ADVICE, COMMENTS APPRECIATED!!!] i (18F) and my bf (18M) have been togther for around 5 years now. he's my world, and we have a really healthy relationship. however, that doesn't stop me from being concerned about my best friend, we'll call her sophie (17F), being around him. initially, it wasn't much. she would talk to him and laugh (A LOT), and id always brush it off because he truly is a funny guy. sometimes she'd tell me "omg your bf is actually so funny", and ask me if he was attending events we'd go to. but then i began noticing other things. recently we were walking to our next class which was upstairs, and there's a set of doors at the top of these stairs. typically my boyfriend meets me at the top of the stairs past the door, but this time met me at the base of the stairs, and sophie was with me. we walked upstairs (sophie ahead, me and my bf behind) and she got to the door. she held it open, which was odd because she was literally in the way of everyone else trying to get up the stairs. but she only held it open until she could get behind us, and proceeded to walk right next to my bf. this is only weird because there was plenty of room next to me and she literally isnt friends with him. she was right up against his shoulder, and there was much room for her to not be. so he got pissed and moved to the other side of me, to which she said "awww you didn't miss me huh?". i was like wtf, as was he. another incident was in class a month ago when she sat down in front of my bf and kept turning around to face him in his desk. she'd just smile at him and turn back around. it was so strange. i think the breaking point for me was the outfit incident. id been facetiming sophie when my boyfriend (who id sent a fit check to prior) texted me saying i looked beautiful. so i told sophie, typical best friend behavior, and was like "omg isn't he so cute" - just me giggling over him and her typical "oh shut up" in her sarcastic joking tone. lo and behold, the next day she shows up to school in an outfit that looks damn near identical to the one my boyfriend said i looked beautiful in. whatever, right? WRONG! she went up to him later that day while i was with him and said, "omg, someone just told me that [my name] and i look like twins! isnt that so funny?". he awkwardly laughed and stated that we really don't look like twins. i later found out that she told another mutual friend of ours that she hoped he would've said something about her outfit. it disgusted me. stuff began flooding in about her copying my mannerisms around my bf, my speech, even my mf sneeze. i confronted her two days ago and she denied everything, saying i was controlling and obsessed with my bf. she told me that if i "couldn't handle him having female friends, that maybe i should be single". i replied quickly that they aren't even friends, and she got all butthurt and said that i was a shitty gf. i talked to my bf later and we made a plan of action together as to how to deal with sophie. we both agreed on sending a text to her. mine discussed my discomfort with how she's been acting around him and asking her to please stay away from him, and his saying the same things but expressing his own discomfort. i sent mine first and she refused to even read it, but when he sent his she read it right away and then texted me, called me, and left voicemails shouting at me and saying im obsessed with her and am ruining her life. aita?