I've had issues since I've been a teenager that I'll go to the grave with; I've wen't very close to taking my own life back then. I think there are two different things; mental and chemical imbalances that affect suicidal people. Some have both.
Growing up we were losers. My mother sold (but mainly used) drugs. Heavy stuff. At one point we lived in an abandoned beer vat in SF with 10 other drug addicts. Some dude from Tennessee (Murray) died from an Overdose a few feet from me. Occasionally she'd get busted and we'd go to foster care. Some of those kids in foster care were 'chemically' messed up; they just weren't right in the head and parents would drop them off. I won't go into details but some of the stuff that went on there was too made up for even television. There were 2 kids that could have killed me without hesitation, they just weren't right and we all knew it.
Anyway, at some point my mother gave drugs to my brothers. Heroin, Cocaine, probably Quaaludes. One of them contracted HIV and passed away, and I still feel being the older brother his death is on me. During that time people really didn't like or sympathize with us, we weren't really likable people. A lot of hate was thrown our way because of the HIV, and because of our social state. We were poor (not I have an old Camry or my Jordan's are 2 years old poor) and just raggedy and trashy poor.
Just before our mom's death she found god, and her stories mutated to where me and my brother were the reason for the death. We left the funeral early, as we clearly were not wanted there and to this day my brother and I will never go into religion.
That being said, I'm 30 years removed from all of this mess and outside of having some obscure personality quirks its just a story now.
The one thing that's always helped me is openly talking about it, but people don't really want to hear it. At 16 I really didn't have anyone to talk to, no relatives, no father, etc so that was a big part of being suicidal.