One, but not until after she left the company. We went from being co-workers to being friends (since we stayed in touch after she got a new job) to being fuck-buddies, and now we’re back to being friends.
Five. (About 25% of my lifetime total…)
The first was a girl I temped with every summer when I was at college; I pursued her for two years without success, but on the third summer she pursued me.
One was my girlfriend, and I got her a job in my company, so it doesn’t really count.
Two were my direct reports; one while I was her manager - very dangerous idea - and I hooked up with the other one after the company went bust.
The latest was the girl that broke my heart. We had to work together for months after she’d left me for another coworker - but I couldn’t tell anyone what I was going through because nobody could know about us. Man, that sucked donkey shit. 
I’ve still not recovered from it. Never again shall I dip my pen in the company ink - or an evil beeyotch.
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My manager at KFC.
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The receptionist at a job in college.