why did she do this despite the fact she is in a relashionship?

[Peter J]

Ok, i was at a party last weekend, and this pretty girl walked in.I looked at her and she did not look back at me, i kept on looking in her direction and she will ignore my looks, so i took it as a sign of no interest.While we were all dancing in a group, i was looking in her direction and still she will not look at me, then as soon as we all finished dancing, i started talking to a friend of mine, and all of a sudden the girl's friend came and told me, she says she likes my shoes.I said, thank you, and when i went closer to her, she said she also liked my shirt, i was flattered by the compliment and started talking to her, i ask her name school etc, then when the next round of dancing started she went dancing with her friends, and said i could come dance with them, if i want.Which ofcourse i did,but i had o leave early, so i gave her my phone to put her number, which she did.Now, i called her a week later, she didn't pick up, i left a voicemail telling her it was me, she called back about 30 mins later, and we talked for just about 4 mins, because i was about to go study, but i asked her for her facebook address, which she gave me.All loooked good until i went to her facebook and saw that her status shows that she is in a relationship, now i don't know what to do,i am really beginning to like her alot.And have no idea what to do.Can anyone advice me