Should I just forget her?

5 yrs ago me and her had a relation ship... i was young and stupid. The first girl who actually cared about me. I ended up pushing her away... we got back in touch and now shes taken, we hang out a lot, but it saddens me because I know shes with someone, and we'll never become anything more now. I still love her, and she said she still loves me. But she said she doesn't think a relationshop could work between us. I thought i could move on and forget her but she has a good hold on my heart and she doesnt even realize it. please, advice? how can i move on.