Drugs. Of course that's not the whole story, but that's what broke the camel's back.
Knew him for over 10 years. When I met him I connected with him. We had things in common, and my friends back then were less than ideal. Abusive, in short. We were both depressed and loved metal, so we had a mutual interest and supported each other.
Now he was always more anxious than I. Terrified of social interaction with people he didn't know, which he corrected with alcohol and medication. Sometimes together. Slowly he went to a worse direction, ending in several suicide attempts and several emergency calls from me and my now wife. Constant worry that he does something to himself again. He did try to get help every now and then, but always quit the therapy after one or two visits claiming the therapist was mean whatever excuse. We know it was just so hard for him and it hurt to know he tried so much but still couldn't do it.
This has gone on for several years. During that time his downfall has been clearly visible. The first signs were that whenever he came to see me and my wife the visits weren't really about seeing us anymore. We usually just sat at our place, drank some beer, listened to music. He couldn't really go to bars or anything, and we didn't care about that, we enjoyed his company. Usually he stayed the night. He was always a heavy drinker, but eventually that was the only thing that mattered, and it showed. Passing out, injuring himself because he was so drunk, drunken calls and messages about suicide and actual attempts. Since he couldn't work because of his anxiety he had no money and we ended up buying his drinks and he forgot about it. I was really offended by his behavior and slowly got more and more against him coming over, but my wife connected with him really deeply and wanted to see him, so I yielded.
Then he told us he'd tried drugs. Synthetic mostly, hallucinogenics etc., not that hard stuff, but I knew it wouldn't end there. And it didn't. The drugs made his behavior worse, suicide attempts more frequent, and just changed him. Wife always noticed from his messages when he'd taken any, and it was often. He idolized drugs and the culture, said that they helped his anxiety and made him drink less. Not really true from our point of view, but fine, as long as he doesn't really hurt himself.
This last year has been the worst. We got some more info every now and then, how he'd tried everything new. When he told about amphetamine I subconsciously resigned myself and knew that he was lost. We were sadder and sadder about his state and more and more offended about his behavior. On his visits he'd suddenly vanish for hours and come back shitfaced and pass out. "Met some friends", according to him. In the end I couldn't be present when he came over, I was so offended and angry at him.
Finally a few weeks ago we got a call that he's at the hospital. OD'd. Resuscitated and alive, but still OD'd, because of mixed use. After that he had a moment of clarity and reason and decided that he needed to stop it. It lasted a week, and after that it's been the same as before.
He has gone from a caring, warm person to a mixed substance abuser and switched to a crowd that mirrored that. Now my wife and I are just waiting to get the news of his death by OD or by his own hand. We've tried everything we can to help him, but we just can't reach him anymore. And it makes us really sad.