In your first post back here, you were saddened by the deterioration of your friendship with H. I wanted to say it then but honestly you do not want to be his friend. Do not settle or accept that role.
That being said it is in everyone's interest that things are amicable. I think long term it will serve you well to really differentiate between being friends and being friendly.
As for your M being saved. Who knows what the future holds, but for now that is not the situation. It could happen but is unlikely in the near future. So park that for the moment and cross that bridge if it comes up later.
I am no expert but I like the jekyl and Hyde mood swings. Yes surely it is a pain to deal with. But it shows conflict within H. That beats 100% hyde. Plus sullen and withdrawn indicate it is more about him than you. Otherwise it would be directed at you in anger or resentment. This is speculation of course but what us sure is that you need to be you regardless of how he is.
Do not let him being sullen affect you so much. His moods seem.to dictate yours.
You think you irritate him.with each interaction. Maybe he does get irritated each time ye talk, but that does not mean it is your fault. He gets irritated. You do not irritate.Analyse your interactions and I am sure you can see that. If not minimise whatever you are doing that irritates him as long as it is reasonable to do so.
I am glad you recognise stating you missed him being a mistake.
Congratulations for finding a job.
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together