Some good posts at Megan's blog about relationships and opposite-sex friends.
Never underestimate the ability of psycho jealousy about completely innocent opposite-sex interaction to destroy a relationship. I went out with one guy in law school (let's call him Guano, because I do) who was obsessed with, among other things, my bathrobe. See, I had a guy housemate, and although we'd dated in college we were by that point totally platonic. But because I'm nice, and not a nudist, rather than walking around in a towel or in skimpy pajamas, I wore a bathrobe. This robe covered me from wrists to ankles, came up to my neck, and was always belted snugly. I called it my burqa; it was even blue. But this wasn't enough for Guano. What if the bottom flapped as I walked down the stairs? What if I sat with my knees apart on the couch? I tried to tell him that it would be harder to see more of me in the burqa than someone could were I wearing, say, a dress, or even a tee shirt and shorts. But he harped on it regardless. He also threw a fit over my going to work-sponsored happy hours which one (partnered!) male colleague also attended.
All this is a long way of saying that if your relationship includes permission slips, there's something way wrong.