Stalkers are like most other obsessives; they start small and work their way up. It's rare someone jumps right into something major. I've seen it enough to see a potential danger when I read about it.
It's entirely possible he may have been stalking you for years
but only now has he become obvious about it or something has changed in him to spark this obsession recently.
Police are a necessity if this continues. Telling him in no uncertain terms to stop it and continuing is harassment and not the idle stuff either.