Firstly, my condolences to everyone that knew him.
Well done in seeking counselling
My brother did the same at 26yo in 1978. My uncle at 82yo in 2001. I attempted in 1996 and my sister in 1999. I've written a lot about this and other topics on this forum.
When my brother passed my parents were angry with his then girlfriend and was the focus of their energies for several months. The reality was, she was found not to be that close to him and she stopped his advances.
I think it's natural to seek out any irregularities in his life looking for answers. From the knowledge I've gathered over my 66 years, I don't think many suicides can be blamed on other people. That's why charges wouldn't stick.
In regards to "evidence" from people giving adverse influences it brings to mind that other bad behaviour that isn't illegal like manipulation, narcissism, verbal abuse, even swearing now all legal but some can devastate lives.
While it's possible his flatmates weren't helpful, I'd focus on their intent and no, they would not have intended such a result. As flatmates, as opposed to close friends they might have suppressed him expressing emotions as they weren't close enough or had their own issues or didn't know how to cope with them or how to help. We here regularly get members asking why people don't understand us with mental health issues. There is one over-riding factor- we can't "see" the illness. That alone places the sufferer in the poor position of being stigmatised and rejected. It's in the too hard basket. Break a leg and you're swarmed with empathy!
My guess- 80% of people are in that category, 10%, try to understand (have empathy), 5% do understand or have an undiagnosed mental health condition and 5% have a diagnosed MI.
I'm bipolar as is my sister and I suspect my late brother. Did you know suicides of bipolar is around 20%?. And the suicide numbers in Australia is greater than the road toll at around 3000 and 80% is male!. So it's very common.
Dear "amonstercalls" I know the hell you are facing. He was graced with a wonderful mum that did no wrong.
NORMAL FOR A MUM
She questions life earned
Searches under rocks upturned
For answers to her loving son
Those queries normal for his loving mum...