Why does he plague me?

There is father at my daughters school who, when I pick her up, over time has increasingly, over the last three years, taken to staring at me. Last year, it was becoming almost unbearable at times. He doesn't do it to anyone else. God knows why, because there are, in my estimation, a number of women much easier on the eyes than myself. I had, on a couple occasions, tried to talk to him to try to gage the situation (maybe I'm naive), but, he was quite abrupt with me. Arms crossed, like I discusted him. At the end of the school year, I talked to him briefly while on a cl trip, and he actually made eye contact. I felt like I was being eaten. I am a very warm personable person. Nobody has ever been so rude to me. What did I do to deserve it? And yet, the next day, I'd feel his eyes on me. I can feel him listening to every word I say to my friends. If I was upset about something, I'd catch him looking deeply concerned, and so on. Almost giving me the impression that he cared about me. A couple of times, I'm sure he over heard me say I was going to the park, and he followed me there. Once just parked, watching, then another time "ping through," but, it strangely felt like some kind of declaration. I was hoping he would have changed over the summer, but, the first day back, he was very anxious to see me. Crap. Like he'd been waiting for a long time. And yet, when I sort of smiled, out of civility, and confusion, he pretended not to see me. And today, he did his best to pretend he didn't notice me (he was with a male friend). He only stares when with a female friend (one of his co-workers). She gets angry with him, and looks at me like she wants to kill me. My husband, who is my heart, doesn't know what to think. I try to ignore him, turn my back on him, but he makes it impossible. The tension from him at times, and hostility from his friend, makes me choke up. I feel like crying. Oh yeah, and, he's a detective. I'm a nurse. And I have a nauseatingly clean record (a.k.a none at all), so he's not "on to me," for anything. I dread going back there tomorrow. If he liked me, you'd think he'd try to talk to me. Geez, at least then I could tell him that the only man for me is my husband. He never has. So, what the heck is going on? It just doesn't seem to end. I feel so powerless.