This isn't really about her, its about you. If you loved her truly, you would let her know your feelings (already done) and then DISAPPEAR until she comes to you clean.
You know its the right thing to do, but you don't have the strength for it. Nor do you have the confidence in your connection. If you did, you would be able to step aside for a while, like HeartIsAching did. She doesn't have the strength either, but then she's dealing with the conflicting pull of two guys and her own messed up emotional state. You, however, have only yourself to take care of.
There are no children involved in this mess are there?
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh