I guess the biggest issue I have with this is the heroine's being utterly oblivious to how members of the opposite sex might interpret her friendliness. Considering she's a HS English teacher... She's not the first overly friendly heroine I've run into who's picked up a stalker either. That's actually kind of a trend I wish authors would ditch - both the implication that being an outgoing person encourages that and the implication that men are incapable of recognizing friendliness as just that.
The H is dealing with issues from his last mission. He...is overwhelmed by her initially. He notices something off though and decides to stick around anyway.
Eventually the stalker outs himself - by attempting to kill her...and the student with a crush. The H and her retired police dog save the day, decides he got through it without wigging out so he's able to function so they can actually have a relationship... Yay?