That's just unkind. Well tu have to decide if tu want her as your friend now o not. other than that tu could ask him why. good luck in what ever decision tu make and never forget there are loads of other boys just as good for tu to find and love.
Sorry for being so critical to start off, but it really isn't something a friend should do. Why in the world would she think that it's okay to steal your boyfriend? That's just not right. At all.
And your boyfriend went along with this? Personally, in my opinion, I don't think he would be your type, then. I think that the right guy would always stick to the one that they love, no matter what. I guess that's sort of picky, considering the guys that I've seen (sorry for being biased and for ranting).
