I agree, and this is the place to vent because those on this site have real experience and empathy about the struggles those of us with difficult children face.
When I am in pain and worried, I want reassurance and comfort, so over the years I would talk to relatives and friends. They care, but they haven't been in my shoes, and like with your relatives, they would tell me to cut contact or feel bad about my circumstances. I think also, that hearing all the awful things my kids did made them wary of any contact themselves.
I also have come to realize that though my reaching out to others isn't true triangulation, I was always trying to win others' sympathy. More and more, I try to bring my concerns to this site, to a therapist, two a trusted friend who does not know my children, and to 12 step meetings.
Regarding being worried about attending Alanon if your son isn't an alcoholic, but has other issues, you can still attend as long as it is an open meeting. Many people with alcohol or substance abuse addictions have co-occuring mental illness .The principles and steps of the program will still be effective for you. My son is an addict with mental health issues. I just speak of him in meetings as my qualifier (the person who led me to attend) and talk about the issues I am facing rather than about his specific disorder.
Sending hugs.