He could very well be having a mid life crisis at his age. I am not a big fan of going dark other than as a last resort technique. There is lots of stuff in Divorce remedy that you can try , what works / what dosn't , keep a diary. Give him space if he wants it but if he wants to talk then let him and listen , listen carefully and validate.
The biggest thing is to concentrate on what you can do , and what you need to do for yourself.
