Yeah, Fearie, I'm relatively new to this and have written elsewhere about what an epiphany I had when I discovered that other people have these strong non-exclusive feelings.
Don't try again to be mono. From what you write I am pretty sure you aren't that. But listen to the more experienced people here because loving a mono is fraught with difficulties because they just do not understand us.
Bless them, they have to take on trust that we truly love them and override all their feelings by acts of willpower. Not sure I could do that if the boot were on t'other foot.
As has been said, things like alcoholism are a whole 'nother problem. If you love him, get him help. This is not from my personal experience, but a drug problem warps your perceptions.