I think that in addition to the fabulous advice thus far that you should wait it out and be a good friend. If you want something to last and to have an ongoing loving relationship then it sounds like it might serve you better to bite your lip until such time as she is free or things between her and her man are settled more.
You might think she is worth more, but she chose him and she knows what is best for her. Right now he is. Not you. You are a good support for her and would be disrespecting that connection and her if you tell her your feelings at the moment. She won't be talking to you anymore if it turns out she is not on the same page as you. Which would be better, to address your desire when you might be able to later or lose her friendship and the chance to possibly be lovers later?
Those are my thoughts on it all anyways.
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