Is she going to give up on me?

There a girl that most definitely is in to me. She texts me pretty often and wants to hang out a lot. I do think she's cute and she has a great personality but I'm struggling to really have feelings for her...I can't really explain it. I still hang out with her simply because I enjoy her company, and we flirt a little but I haven't made a move because I just don't feel the drive to do it, but I know I should. The other day I wrote on another girls wall about hanging out but it's because she is my best friends ex and we are very good platonic friends I wouldn't date her but I think the girl in question believes I'm into her. I think my reluctance has to do with the fact that I've been getting over a girl I was off and on with for years and I'm getting there but I'm not completely over her yet. Should I just give it a shot with this new girl even anyway and hope that feelings develop? and if I don't act quickly is she going to think I'm not into her and give up? Thanks to anyone who answers.