Im in the same situation right now. And i have asked over 5 questions on here and everyone of them say that the one thing that i can control is staying in contact with her. SO my opinion for you is to do the same. Just stay in contact with her but dont get too pushy. Do the things that she wants to do. Like if you are talking and you see that she wants to stop talking, then stop the conversation. Make her feel good around you.
I've been in the same situation. The girl I had a crushed on "had" a boyfriend. She knew that I liked her, so I took her out to the movies/mall, talked/text her, and helped her if she needed, basically do stuff that she'll enjoy and have. She broke up with her boyfriend. We're still friends though. I'm still waiting for that perfect time to ask her to be my girlfriend and hope that I'll be with her someday.
For you, just keep socializing with her, hang out with her, and take her out, but as friends. Don't bring up her boyfriend around her. If you truly love her, you'll wait for her. And if she sees that you're really into her, maybe she'll break up with her boyfriend to actually be with you. Who knows? Wish you the best.
Just wait for her to break up with him. Don't do /anything/ romantic or sexual till then.
Whatever you say you are in love with a fantasy.You love the girl you imagine her to be.
Enjoy the fantasy while it lasts but don't let it stop you seeing the real live girl that is in front of your nose.