Since you don’t want to ask her out because she has a boyfriend, and you don’t want to screw up her relationship, you have to stop seeing her and move on. You can’t have it both ways. 😕
You’re trying to twist everything in every direction instead of being clear with yourself — and her.
Read the book I’ve written for men, Date Out of Your League, [url]https://www.askapril.com/relationship-dating-advice/date-out-of-your-league.html[/url], so you understand more how to win with women. After you’ve read it, let me know if it helps.
Good luck! 😀