My question is this- what would you do differently if you 'quit'?
If you let go of what your H is doing and stopped rooting for him to come back towards the M, what would that change in your behavior? Would you stop trying to improve yourself? Would you start seeing someone else to comfort yourself? Would you tell him off because you no longer cared what he did so you want to hurt him like he hurt you?
In my opinion, there is no reason not to quit. In fact, I think quitting is a great choice...provided that you are quitting holding on to H. If you can quit while still making good decisions for you, while avoiding the burning of bridges, and while being your best self, well I feel it is the best for you, AND it is the best chance you have of letting him complete his journey as he won't have to create more distance to get away from you (you'll give him the space he wants).
I don't know if I said that very well, but this is what I see as the eventual next stage. Giving up hope while still walking the DB path.
Me:38 XW:38 T:11 years M:8 years Kids: S14, D11, D7 BD/Move out day: 6/17/14, D final Dec 15