You're being strung along like a prize bull with a ring in its nose.
If she wanted to be with you then she would dump his ass and be with you.
You wont' do this but you should stop seeing her, stop talking to her and stop pinning your hopes on her. She knows how to reach you to tell you when/IF she's left her BOYFRIEND.
You might be shy but you're also stupid to allow yourself to think you're "in love" with someone who hasn't yet left the sap she's cheating on at home. Take back your self-respect and tell her you're moving on and to contact you when she's single. Even if she does contact you IF she becomes single ...
How will you ever trust her not to cheat on you if she ever leaves him? ...
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion