Why does she act this way towards me?

Long story short there is this girl that I know and as of lately she wants me to be around her all the time and when I am not around her she pouts and asks me why wasn’t I with her or where I was. Naturally that would make one think that they like you but the thing is that I had heard that she liked someone else. Why would she act this way towards me and want to be around me all the time yet she has feelings for someone else?