Here is what has saved me. I no longer accept that D is an option. Sure, W continues to threaten me with D, it's still an almost every other day thing now, but I've realized it is just W venting her feelings, not planning action. I know that there is nothing I can do to stop W from filing, but I do not have to participate in any conversation or thought process that includes planning for D. I try to live my life the way I want to live it, and don't even think about D.
Our Ws have a lot of issues they need to deal with, and their method of dealing with them is by talking. They say what they are thinking, without thought of the consequences, end result or impact their words will have on you. Probably the best thing you can do is exactly what you are doing: keeping it together, and just being a solid rock for W. She's going to flail around for a lot longer, as long as she knows she has you to count on, she'll eventually stop flailing and eventually get back into stride with you again.
It can be very hard at times, and often overwhelming - this is when you having GAL to occupy yourself and a strong faith in God will carry you through. Drugs are not the answer - all they do is postpone your minds ability to deal what needs to be dealt with. It is much better to occupy your conscious mind with diversions and God's peace and allow your unconscious mind to continue to process things. Taking a drug to dope your mind into not having the capacity to deal with this stuff is BS.
