Do you have one? I do.
The work boyfriend is the guy who you hang out with at work, going for coffee's, lunch, smokes etc. You chat on MSN and gossip about co-workers.
You are both in relationships or married, but if you weren't....
Anyway, my WBF and I don't work together and never have. He is a supplier to me and we just happened to hit it off immediately and thus became friends outside of work. We go out for drinks and lunch and he came to my wedding. He complains about work and life and I do the same to him. We offer each other a sympathetic, other-sex ear.
My marriage doesn't suffer as a result of my WBF. In fact, my husband doesn't care about our 'relationship' at all. I guess our marriage is solid enough for any stupid bouts of jealousy like that. I'm not sure what my WBF's wife thinks of us. To be honest I've never really met her, nor has WBF met my husband. The only exception was the brief time we spent with them at our wedding.
I'm about to head out for lunch with him right now. We should have gone out drinking but things have not worked out for us to get together in the past month or so and thus we are conceding to lunch instead. I'm sure a pint of two will be consumed, but it is not the same thing.