There is so many variables on this topic that it's difficult to give one answer. A man who never had suicidal thoughts after a breakup isn't excluded from it ever happening to him in the future.
MENTAL ILLNESS:
Some men have underlying conditions like severe depression, codependency, lack of self love, or a mental disorder. Women crushes his blue pill love fantasy, man spirals into deep depression tricking himself into thinking there is nothing else to live for. So the only way to take the pain away is to permanently shut off the brain.
CLUSTER B:
Imo it is mostly due to Cluster B/toxic women. Which we know have driven men into suicide. The one question I got asked the most from all the men I helped over the years was why do all these toxic women seem to be reading the same play book on every man no matter what part of the world they are in. The answer to that is because the script works. Love bombing, devalue, discard is a highly effective form of mind control. I helped people from all over the globe and almost every single story was about the same, down some to fine details that rarely mentioned.
After all my years of research and my own experience I have come to the conclusion that this is on a spiritual level. The reason why I came to that is due to how many men told me the Cluster B women either openly or secretly worshiped the devil, used God in their excuses to cover up lies or cheating, used the bible to manipulate them into thinking they were religious, used churches to get their victims, had 666 or demonic tattoos, and some other things that would sound crazy to most. There is many more examples I could give but thats more than enough. The devil uses mans biggest weakness, the flesh. It's also not a coincidence that these toxic women are all beautiful and give out some of the most amazing kinky sex, that the man ends up falling for the scam and lands into her web of destruction. Even the strongest of men can get taken down by one of these women.
I also believe they pass on the spirit of suicide. The man either comes out the stronger/strongest version of himself or ends up 6 feet deep. It's also very common once the relationship is over they develop PTSD like a solder coming home after war. PTSD is known to cause suicidal thoughts which can later lead to suicide.
Then you have men who to turn to drugs/alcohol to deal with the pain after coming out of a relationship Cluster B or not. I've read & heard so many stories of overdose deaths as a result. But you don't see that connection being mentioned in the headlines.
MIND CONTROL:
Mind control is very real, effective, scary, evil, and it can kill. Trauma bonding is a very powerful by product of abuse. Long term mental and emotional abuse can also cause brain damage. Whether they're aware of it or not, Cluster B's are masters of Mind Control. When you study each of their tactics, it's purpose and outcome, only then do you realize how demonic it is. One thing rarely talked about is how this kind of abuse can lead to strokes & heart attacks. The extreme mental/emotional abuse causes so much stress, the mind & heart "can" get a fatal overload. Not a lot articles on that type of mind control death. Hopefully in the near future it will be talked about on main stream media. I know it's happening a lot more then people would believe due to it being difficult to make the connection or even think is even possible.
They are silent killers, no cuts, no bruises, no blood, no forensics, all mental warfare. Example of a different type of MC death, the Michelle Carter case from 2014 where she was able to get her male friend to commit suicide through text messages. There is a lot of little details that show just how evil her true intentions really were. Those details should have been used to get her more time, cause in the end all she got was a slap on the wrist (imo). It's just too unbelievable for 99.9% to truly understand, relate and comprehend just how powerful it is. To keep it short, one detail being she manipulated his friends by telling them he was out of town so they wouldn't contact him in hopes they would talk him out of killing himself.
LOVE:
You have some men who weren't loved as a child. When they find a women whom they fall in love with, they become addicted to "love" like a heroin addict to his high. When the women leaves him, she takes away that love, your "addiction" with her. Now the man is left feeling hopeless, depressed, nothing left to live for. The same way a heroin addict feels when that high is taken away. Addicts as we know are no strangers to suicide.
At the end of the day "love" is what we seek. The connection of love between two humans is one of the greatest of highs. When we find it and experience it, we feel alive! One of the most powerful of all emotions and stimulation the brain can experience. Love, is the one thing in a persons life they strive to find, to feel, to chase, to embrace. Bad things happen when that love isn't given to you, betrays you, leaves you, abandons you, or someone comes into your life to intentionally steal it from you.