OP I suggest you go to therapy yourself to find out why you believe you need him in your life.
I think you are part of a very unhealthy dynamic here. You need to figure out why you want to play the role you are playing -- healing this man, trying to make a silk purse out of a sow's ear, pushing the square peg into the round hole.
Do you hope deep down that you are special enough to tame his demons?
Are you seeking some sort of validation of yourself by embarking on this healing mission?
I don't make excuses for him...
This is not necessarily true. I think you should look at your words here, at the snapshot you have provided, since you have done that in the case of your H.
...and of course all of you are strangers to him and me
This is defensive. You are defending the relationship.
...and of course you don't have any knowledge of our history.
You need to try to figure out why you think there is something exceptional or special or unique about this relationship of yours. Yes to a certain degree every unhappy home is unhappy in its own unique way, and all happy homes are sort of similar, but please ask yourself if you are invested emotionally in the specialness of this relationship (and in the role and reward you seem to have identified for yourself.)
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Please also consider the idea that part of how Cluster B personality disorders present themselves, and part of how they damage their victims, is the sheer irrationality of their words and deeds. This irrationality is an affront to others who are reasonable, rational and 'normal' for want of a better word, especially those in close and intimate contact with disordered individuals. It is maddening, and the brain and spirit of the victim can't make a dent in it at all.
It is very much a predictable response of a victim or this irrationality to place your hope in counselling, or the power of psychologists, or some other supremely rational force (for instance the collective judgement of a majority of posters on a MN thread) to try to effect a change in the disordered individual. The fact that you have chosen this option tells me that on some level you realise that you are dealing with profound irrationality and your mind is desperately seeking reason and rationality as an antidote. You have already tried to explain it all to yourself - he is depressive, etc.
Please know that Cluster B disorders are extremely difficult to 'cure' and also that they inflict a huge toll on their victims regardless of age. Whether you think you are hurting or not, I really, really urge you to seek individual counselling for yourself and ask specifically for help as a victim of someone with a Cluster B disorder.