This girl seemed to like me, but now seems to be ignoring me?

[Mustang]

So, there's this girl in my university. I think she liked me. You know, the eye contacts and all that jazz. Usually I am fairly good at deciphering such indicators of interest, and I definitely think that she liked me. I didn't really make an effort to talk to her. We talked a bit once or twice, but that was it.

However, a few days ago she started to ignore me. Would go away if I came into her group, etc. I sent her a friend request on facebook, that is also still pending, been a day or so. I also found out that she is currently in a relationship, and I didn't know that before. But, I don't think that she knows that I know that she's dating someone.

Obviously now that I know she's not single, I'm not going to do anything, but I'm still confused why would she act like this.

[Summertime]

Maybe she saw you making eye contact with someone else. You men are so insensitive to our needs and desires and feelings.