Warnings of a death hex? This guy is angry but has probably never cast anything. He is trying to scare you, threatening you with magic so you will know the curse is going down is pure intimidation, using your own mind against yourself.
If I were that angry about a breakup I would keep it quiet and strike when they’re at their weakest without a word to my target.
This is like a psych op using what some people call headology, the principle that what people believe is what is real. This is used by witches to earn respect or at least fear and operates through the targets fear resulting in a self imposed curse when the practitioner in question doesn’t have the skill necessary to effect much change themselves.
If the threat of a hex works on the target they effectively curse themselves while thinking the person/s who made the warning are responsible.
You’ll find plenty of posts around here on this: