Emery Ross in Beth Loughner's Lessons of the Heart fits the mold perfectly.
Emery falls in love quickly.
So quickly that Emery makes one big mistake he still regrets. Because of this, Emery believes he can't trust any woman. Or more precisely, he can't trust any woman he could fall in love with. This fear worsens when he falls immediately for Kayla Murray. Constantly keep watch on the object of his affection, of course.