I know I got attached far too quickly - it's just that, when you spend so much uninterrupted time with a person, especially for someone as emotionally-driven as me, it gets a little hard to stay... aloof, for lack of a better word? I just find it really difficult to pace myself when it comes to that sort of thing, so I suppose that in a sense I brought this whole situation upon myself.
My friend was very open about the whole thing, also: she wouldn't have got with him had I not told her I was okay about it. She's still feeling really guilty about it right now, but she needs the stability far more than I do. Doesn't stop if from hurting, unfortunately!
Thanks for helping out, it's really appreciated. I feel like such a whinge, haha.