I think I’ve first heard this in a Church but they didn’t use the word “fuckmate.” Three months relationship is barely past the performance stage. You're still showing your best self, hiding your worst habits, and testing whether you even like each other beyond surface-level attraction.
So what counts as a relationships start when the masks come off. When you've seen each other stressed, broke, sick, frustrated, and still choose to stay. When you've had your first real disagreement and had to figure out how to communicate through it instead of just walking away. Three months? You haven't even scratched the surface of who someone actually is.
And calling every short-term situationship an "ex" also cheapens what a real relationship is. If it ended before you even got to the "do we have a future together?" stage, it was just dating. And dating is supposed to be the trial period where you figure out compatibility; not the relationship itself.
So yeah, if you dated someone for nine years and were married for two decades, you've been through enough seasons with women to understand patterns, communication styles, emotional needs, and how relationships actually function long-term. Someone who dated three different people for three months each has barely scratched that depth.