Why would the same guy drive by my workplace multiple times a day?

I know I am going to sound like a crazy person, but can't make this up. A guy I know (we hooked up once) drives by my workplace almost every day and not just once, but multiple times through-out the day despite the fact that we are both in commited relationships with other people. I am familiar with people "orbiting" but I don't understand why they do this. To me it's odd and I don't understand the reason behind it.

Why would the same guy drive by my workplace multiple times a day?
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