My WORST enemy STOLE my girl. What to do???

well, about 4 years ago, i developed a crush on a friend of mine, unfortunately, im like a troll, and shes like a perfect princess. so obviously i had never told her my secret. we have been great friends since forever, we're always hanging out, going places. but always just as "friends." and im always seeing her go in and out of relationships with "prince" guys that always end in heartbreak. and i was always there to comfort her. so as this year rolled around, i decided to suck in all the courage i could muster and tell her of my true feelings when, of course, my WORST enemy decides to ask her out (he is prince lke too.) and here is the worst part. they are really getting serious. though i can tell that there is doubt in this relationship, and my worst enemy always treats her kinda bad. she loves him and would never break up with him, and he knows he has a prize catch. he would NEVER let her go.