[TheCrowing]

You really do have to communicate.

Although this may be the only way that she's happy with her situation at home and in public, it doesn't mean that you're happy. Yours is just as important as hers. Talk to her about it. If she says she won't break up with him, you have to be the one to set things straight. I understand that you love her and she's the one you really want to be with, but if she's putting you in a position that makes you feel this bad, you really have to do something.
Also, do you not get a bad feeling about the cheating? Personally, I could live with hiding a relationship, but I could never deal with the person I love being with someone else in public just to please her family and friends. I wouldn't be able to take that in an innocent way. It's cheating.