Well, that already happened. Kind of. Also, she's been on other dates, but didn't end up getting involved. We're both perfectly cool with it. Like I said, there is no emotional/romantic attachment. Why is this hard to believe?
[edit] At any rate, the main point I was making was to keep the relationship low-key, if you don't want it to affect your work productivity.
edb is skeptical (as am I) because people are good at deceiving themselves, e.g. I'm not racist/sexist, I can quit drinking/smoking/snorting anytime I want, all my relationships fail because the other person is a jerk/bitch/slut, my code contains no bugs. Until the test coverage is high, your confidence at how correct your code/assumptions are should be low.
Some skepticism is fair, but notice that - because non-monogamous relationships are somewhat socially unacceptable - we'll perceive them to be less common than they are, because people don't talk about them. So randomwalker's situation might be more common than you might think.
[edit] At any rate, the main point I was making was to keep the relationship low-key, if you don't want it to affect your work productivity.