friend problems

My best friend moved to Kempsey at the beginning of this year. she and i have always been very close and even when she moved we still talked all the time. we help each other through bad times, no matter what.

but recently my friend has started hangin around with a guy who she really likes, they have fooled around with eacher other (nothing to serious) and she wants to have a relationship with him. the problem is that he has a girlfriend who is in Brisbane.

i have told her that what she is doing is wrong because he is in a relationship (he won't break up with his girlfriend for her) and if she keeps doing stuff with him someone will get hurt. she of course says that he is the one for her and that it won't hurt anyone because his girlfriend will never find out, she is convinced that she will never have a good relationship and that she should stick to sneaking around with guys.

anyway, we had a really big fight and i told her that i can't support her in this matter and that i don't want to talk to her while she's doing this.
the problem is that she ad i have never gone mor ethat a few days without talking and its been well over a week. i want to talk to her again but i don't want her to think that what she's doing is right.

am i overreacting ?