I know, it seems like a horrible, unmentionable topic except it isn't. Suicide is merely death by one's own hand and death is a fact of life. Most people seem to be very afraid of death and dying and particularly afraid of talking about it.
Yes I often think about death, dying, suicide, about my own mortality and that of those I love and love me. I have tried to end my own life and failed (obviously).
Having tried and thought about suicide so much has made me understand that when it happens there is no fault, no guilt, no reason to be found, it cannot be explained by those who are left behind, it is distressing, unbearably sad and so painful.
It is also true that when all you can do is to try to end your life you feel so alone and there is nothing else around you, everything seems dark and you just want the agony to end so if your attempt failed you feel extremely shit, to the point of not reporting it to a dr or a friend so you get to feel even more alone.
I do not believe every depressed person thinks about suicide, perhaps they have a 'mortal wish' i.e. they wish they were dead but not necessarily make plans or think about acting upon it. That desire to be dead cannot be told so easily to others because most people think suicidal ideation and mortal wish are the same when in fact they are very different, however one can easily end up committed in a Psychiatric ward for saying 'I wish I was dead' so no wonder many with mental illness do not disclose their deepest angst and thoughts so easily.
Depression makes you very irritable and I think this combined with fear of being judged by others who do not understand what you feel makes many of us withdraw even more, so in effect even more alone and therefore we don't talk about 'it'.
People who are healthy and have never had depression find all this very hard to understand and often don't know what to say in which case is better not to say anything and only ask if you really want to hear the answer, make time and brace yourself, it may not be as bad a chat as you feared or it may be just about the most confronting talk of your life, only offer help if you are willing to help and never out of duty, there are professionals who can help you sort out what kind of help you can be and please for the love of universe do not say: 'you're not doing so bad, there're people out there who have it worse, think of Africa' that certainly doesn't help.