She gave me her number, but has a boyfriend?

[Wesley]

So i got up the confidence to ask this girl for her number. I have caught her lookin at me, we talked and when we did she never stopped giggling and smiling and being shy but still attentive to the conversation. So i caught up with her a few days later and said "Hey look i think you're really cute i'd like to get to know you better. Can i get your number?" She starting blushing and giggled more smiled and said "sure" put her number in my phone. I never have confidence to do these sorts of things so that was HUGE triumph for me to be honest. Anyway i get home and i got 5 minutes to kill so i look up her facebook. Creepin i know, but i was curious. It said she was in a relationship with some dude i couldn't see for how long the last post was like December 16th and her profile picture was them two just sitting there smiling not kissing or anything like that just smiling. Her profile is set to private so that's all i could see. I went to the dudes profile, same picture. Im confused. I clearly showed interest in her with the way i asked for her number. Why give it to me if you're seeing someone? Why not say "I'm seeing someone" or some shit why give me the number? I never do anything like this because i have low confidence to be honest and its even lower now because i feel like she gave me her number out of pity.