second guessing

I have had a serious bout lately of second guessing which is toxic. There is still a part of me that thinks .. well I can change the outcome or I could have changed the outcome if only we had done x or y or z.  This is ridiculous and destructive. However it seems to be a particularly painful part of the process. It is the kind of thing that if you could run away from it you would as if the second guessing piece is an avalanche or a flood - escape is possible.  It just isn't. Tom can't come back as he has crossed the great divide and I can't find him for the same reason.  So if any of you who have been reading this have a cure for second guessing let me know.  So far I can only find physical labor.  I am not used to having something be so well.. out of my control and permanent.   Rationally I know Tom made most of his own decisions and I was the support. We were in this together and I guess we still are . It is just harder.