I'll make a long story short.. I'm 19, and she's 20.

So me and my ex were really good friends, and all of a sudden we dated for a few months. We had our ups and downs. We started dating/seeing each other last year around this time. Now, April 2011 we ended our relationship for good, but found ourselves being sex buddies.

She eventually dated some guy through may 2011 until mid June. Then he cheated on her, of course, she came to me. I supported her and helped her out. We were seeing each other for about 2 weeks, yes we did end up having sex and what not. Everything seemed cool until I realized I was getting feeling back for this girl.

Then after those 2 weeks and we had a talk about what we were doing and how we went from hating each other to, having sex. The day we meet up and talk about her problems.. after that talk she's been getting really distant from me, and I can see why. But we talk every day like small talk hey how are you what's up. We haven't hung out for almost a month now, and every time we talk we end up getting into a small argument because someone told me she started seeing another guy and I called her out on it.

We agreed not to talk on the long weekend that just passed and yesterday we tried again but just argued because she told me that her and this guy have hooked up a few times but its nothing.
Now here's my question.. I don't know what to do because she tells me all the time she wants to really be my friend and all. But she's worried we will end up having sex. BUT I can not be her friend if she is seeing someone. I'm not jealous its just the fact she's with someone else and it irritates me.

Have nothing more to do with her-she's using you as her back up call-bad place to be.

No you can't be her friend so avoid the confusion and irritation and go no contact.

I figured as much.

Just hard letting a good friend go because of such a weird messed up situation. But I guess that's life right.

Yes, see it as a learning experience and move on to bigger and better things.

Good luck.

All right so,
I sent one last message to her just making sure our friendship didn't end on bad terms. I hate burning bridges. I asked for her not to reply but she did and I didn't answer it.. all she said was OK, 'if you can't be friends right now I respect that, ill see you when I see you, and if you ever need anyone I hope you know I'm here for you :)'
Guess its just time to move on

Yes it is.

Time to move on to bigger and better things.

Yep, time to move on for sure. You tried to build a relationship out of FWB, and got to deeply involved and wanted more, but she didn't. It happens when feelings are driven by lust.