Viktor Frankl is a great voice on personal responsibility--e.g., your wife's choice to cheat was hers alone and not controlled by you or OM, your choice to "respond" or "fight" instead of detaching was yours alone and not controlled by your son or her. Frankl was a Nazi death camp survivor--who wasn't broken and even managed to find some satisfaction there. In Man's Search for Meaning, he writes: "Between stimulus and response there is a space. In that space is our power to choose our response. In our response lies our growth and our freedom." An absurdly funny film about the holocaust that focuses on the indomitability of the human spirit is "Life is Beautiful" by Roberto Beningni. Add one of these to your queue when you have time.
I'm rooting for you and your son, Steve, let go of this destructive person you're holding onto. Find love ("I see you, I value you.") and let go of co-dependency ("Life is terrible without you.")