<human>: He and I are both recently out of 3 year relationships. 
She added and began talking to him VIA Facebook a week and a half before I did.
She's dating other guys, having sex with at least 1.

We all hung out one night - she invited another of her crushes and they both were very hands on with each other. Neighbor spoke with me the whole time, insisted on buying all of my drinks. It was all friendly and at this time I was under no impression he liked me.

 I in fact was under the impression he had a girlfriend still. He had invited himself out, and it was odd for me to turn him down so she and I agreed the relationship we had with him should only be that in which we would feel comfortable with our boyfriend having, for instance.

The next night he asked me to dinner, and I had to bring up how I had a problem with him asking me out while he's in a relationship. This is when he told me they aren't together anymore.
So I mentioned this to my roommate, and she isn't talking to me now. Before I had agreed to go out with him, I wanted to make sure she felt comfortable with it.
She told me if I was looking to make sure I wouldn't hurt her feelings that it was too late and I already have.

In all honesty, I didn't think she would get this angry as she had a couple of guys she's seeing already. 

Am I right in feeling that she's being unfair?

Condense the text into a few key points
<bot>: We both crushed on him, she has other boyfriends, he shows interest in me, she hates me for it.