I'm not the best DBer on here so take what I say with a grain of salt.
At one point you will find that you need to figure out what you are willing to live with. She insists in living in a sham marriage, in which she doesn't even have to pretend to love you. They way things are going she will not have any incentive to change for you. (I learned this from personal experience).
I imagine every time she tells you that she loves OM over you it's like a dagger to the heart. I know from personal experience to be treated like a chump in your own home. As for her being good to you, it's all avoidance. Mine does it too.
She is currently in a very heavy fog, since she can't even see how this "so called" wonderful OM, sees their future as a financial transaction.
Lose too much money from the D?!!!! I thought they were in love. That doesn't sound like Mr Perfect if you ask me.
So my advice is to DB and GAL, become a better man. Once you become a catch she'd be a fool to lose, go ahead and let her know how the current sitch is unacceptable, and that you are willing to let her go on her own. The way things are going you are enabling both her and OM to keep their relationship going. So yes I am saying to let her know that a D is imminent if things don't change.
Now all that being said how you go about it is of utmost importance. You want this decision for her to be SO HARD that she picks you. Not so easy that she runs to OM, here's my advice.
1. Keep improving yourself, make her think she'll regret losing the "new you" she's always wanted.
2. Find the appropriate time sit her down and start the conversation.
3. Tell her that you love her, and that you don't want to lose her.
4. Tell her that Despite you loving her, she has decided that she cannot love you back.
5. Tell her this really hurts you, and how it has pretty much destroyed you.
6. Tell her it's not fair for you to continue living like this.
7. Let her know that you know that she is unhappy with you, and deserves a chance to go make her life, and follow her heart.
8. Let her know that it is her decision whether she stays or goes, but that you do not see either of you being happy with the way things are.
9. Remind her that you only want her happiness.
Ok all that being said, delivery is key here. There can be no anger, or no clinginess on your part. Just let her know that the you know the situation is bad for the both of you, and that you want both of you to be happy. There's also a chance that she will just flip out, don't fall for that trick. Just take a breath, relax, and calmly keep going. If she walks out, let her go, re-engage within a day or two.
I read your thread and I know that you are scared of her walking out. I understand it took me 3 threads before I got the strength, and even then I gave a whole lot of concessions, that others think I'm a fool for having given. On the other hand it sounds like she is over a lot of the initial anger and stubborness common with the initial drop of the bomb. So it might be time.
Remember the key here is to stack the odds in your favor, so be good man, and take advantage of the fact that OM is not fully committing.
Don't tell her this but she needs to think:
"Wow he'll divorce me for my happiness, and OM won't even divorce his W for his and my happiness...I think my H is a better man."
Finally I read a part about you doing a lot of favors for her, on top of that she seems to be walking all over you. I recommend a book called No More Mr Nice Guy. It is very eye opening. I recommend it, because it helped me and I am in a similar sitch.
