First of all, I give my deepest condolences for this happening to you and your loved one. Before reading this, I had not realized how utterly devastating it would be for my loved ones to had lost me when I experienced my most horrific trip on shrooms. It will be hard for anyone to understand why this awful shit happens to great people unless they've experienced a "bad" trip themselves, so let me explain to you what happened to me. It might offer some insight as to what your boyfriend may have gone through while experimenting with shrooms.
It was my birthday. I was born on April fool's. I decided I wanted to have a party and trip on shrooms (after only trying it once before with only my boyfriend and just the two of us at our house). My guy invited friends over to celebrate, and one of our friends gifted me a shroom chocolate which contained 2-3 grams of the substance (first time I tried 1-1.5 g). I ate the whole thing, completely unaware of the events that were about to unfold...
Everyone was having a great time until two of my boyfriend's friends started an argument, which escalated to the point of yelling/screaming and startled everyone in the house. The energy throughout the house shifted almost immediately... and that's when I began to hear things. Terrible things. Things about myself I'd only shared with my boyfriend. I was hearing this shit in the voices of our "friends" too, I couldn't tell if they were really being said or not. In my house. On my birthday.
I asked my boyfriend if I could speak with him alone upstairs, and proceeded to ask him if people were saying mean shit about me. He told me they weren't, but from upstairs in our room I could hear terribly awful things being said; he couldn't. With everything that I heard I felt a stabbing pain in my abdomen, terror set in, and I couldn't find myself able to go back downstairs and socialize with our "friends." A few people from the party came upstairs to check on me and see if I was okay, one of them offering such bad advice I felt like I was about to stop breathing. I was enduring such emotional torment that I thought it useless to live on. Especially hearing the shit everyone there had to say about me, which included hearing my lover/confidant spilling all of my insecurities to his friends who were all laughing about it. I felt like a fucking joke on my birthday. I wanted to run and jump off a bridge. I wanted to stop breathing. I tried to cover my ears but I couldn't stop hearing them and the painful shit they were saying. Tears poured from eyes. I thought everyone was in on this huge joke, because everyone that came upstairs told me they couldn't hear anyone saying anything horrible at me downstairs...
Coming down from my trip I was completely shattered. I couldn't tell if I had just experienced ego death in or from reality. I felt horribly sick, but still managed to drag myself to work that day. I was so confused and hurt about what went on. I felt I couldn't trust anyone.
It's been a month now and after many apologies and positive affirmations from my significant other I still don't know what truly happened that night. I've tried to dismiss it but the things I heard ring clear as a bell whenever I'm slightly triggered by any social situation. I realized though, after this experience combined with other bad but less severe trips on LSD, that overall my anxiety, depression, and paranoia has significantly increased. Some days I can almost manage, others I feel like driving my car off a bridge. So, I've come to the conclusion that I must avoid hallucinogens at all costs.
I wonder if your boyfriend experienced something so horrific during his trip, perhaps bringing his worst fears out to play, that it drove him to end his own life... I'm so sorry for your loss.