<human>: Could you distill the essence of the text into 1-3 sentences?

Okay, here goes.

Met a girl in college and became pretty good friends with her. There was never anything romantic going on, and we didn't hang out too much, but we were very friendly and put on plays together in the theater department. As time went on we both became members of the local community theater and continued to work together there. 

About a year ago, she started acting a little less friendly. I worried but I just assumed that she was going through a rough time or something. As time went on, she became more and more distant - but just toward me. She'd avoid eye contact. She'd give big hellos to everyone else in the theater and a simple "hi" to me (or she'd just ignore me). Now, she only speaks to me when she absolutely has to for show reasons, and it tends to be very blunt and curt. Last night at a rehearsal, she met eyes with me for just a moment, and the look she was giving me I can only describe as revulsion.

After last night's rehearsal, I decided I should figure out what's going on - starting with a text to her boyfriend asking if he knew if I'd done something wrong. I'm good friends with him as well (in fact, better friends than I was with her) and they had been dating since before I knew either of them. I figured if I had done something she would have told him, and if he felt like responding he could. I haven't received a response from that as of yet.

So now, I'm really upset with myself - I have no idea what I could have done to offend her so badly, and what would merit this behavior for so long (and why her hostility would increase over time). I would confront her directly about it, but what if I did do something terrible without even realizing it? I feel like if I had done something and been oblivious then confronting her would make it all the worse. We work with each other quite frequently, so resolving this on good terms is important to me, both in a business and personal sense. What's more is I tend to be good friends with practically everyone I meet; it makes me really unhappy when I offend someone in any way.
<bot>: A friend of mine has slowly grown hostile over the past year, no idea why, don't know how to confront her without sounding like an asshole but I want to make it right.