Not enough history here for an outsider to conclude anything about someone's propensity for suicide, but did you ever consider the possibility that because you are leveraging a gender-biased family legal system to take both his children and his money, statistically speaking you are about 85% likely to prevail, and because of that, he may be a tad depressed? Don't overreact and try to make more out of his message than it is. Ask yourself if you are making this into a big deal for some extra leverage for your upcoming hearing? He should see his kids unsupervised - it's about them getting to spend quality time with their dad, not you overreacting and controlling every aspect of his and their life. And hun, it's not "visitation" - that's a term used when you "visit" someone in prison. Are your kids in prison? If not, it's "parenting time". I wish all the best to your children and that they may have equal access to both their parents without undue interference from you.
Why would you think that you have the right to allow or deny him access at all? Would you be ok with someone treating you that way?
You can't and shouldn't gatekeeper the kids away from their own father. The relationship he shares with them is his and their right...just like the relationship they share with you.
Of course the children should see their father as much as they're seeing you. Especially if you care about their emotional well-being.
Based on your post, its not clear that there's anything at all wrong with your ex. Maybe he's upset that you're controlling his ability to see his own children.