I'm having a bit of a problem letting go... any advice?

i fell out with the ex i loved the most but i never stopped loving her. for 2 years i continued to love her though i didnt put my world on hold for her return. i told myself if i really loved her i would accept that she couldnt be here bcos she was happier somewhere else. then a year later our paths cross and her feelings for me have returned again. of course i love her just as much but shes in a relationship and i dont want to come in between. so im acting as nothing more than a friend to her. to me if its meant to be it'll be somehow someday. it just kind of saddens me to have to continue letting her go right now when i know full well she does have feelings for me but isnt acting on it. any advice?