I have a similar situation to Effic. But it's also completely different!
My dh isn't a blokey bloke if you know what I mean? He's quite sensitive and sweet. Not what you'd call a manly man (not camp though, I know some straight men who are incredibly camp!) But more like a sweet, geeky man, who's more interested in star gazing than football or going to an art gallery than the pub. I guess, cultural (?) Is the word, but he's not pretentious!
My dh has a great female friend, who he's known since high school. She is incredibly successful in her work and has an exciting but stressful job. I know for a fact that she pursues married men - she's just ended a relationship with a man who left his wife for her (he was an abusive arse and both she and the ex-wife are much better off without the bastard) to date another married man. She is a messed up individual, who I wish would meet someone nice who respects and loves her, but unfortunately she needs serious counselling/psychotherapy before she does this. It's truly sad.
I do not however have any qualms about the friendship my dh and she share. Not because I'm such a big hearted person or because I'm a walk-over but because even before my dh and I first got together (we had known each other for a long long time as friends way before getting together) I asked him how he felt about her. His answer was "it would be gross, like sleeping with my sister or something!" - I expect she feels the same about him - for them, they're more like siblings. They have had ample opportunity to get together, and haven't. I trust them both. We're even talking about going on holiday together next year (with a newly single male friend and his dd as well).
I have asked dh about his other single female friends, and he's always said "we're friends, that's it. They don't see me like that, and I don't see them like that" - these are women he worked with years ago in a bar who he just had fun with. When I finally met them, I actually really liked both women an awful lot! I didn't feel threatened by them in the slightest.
I might have done if they'd flirted, but they didn't. I might have felt threatened if I didn't trust him implicitly.
I've spoken to him about cheating, and his stance is that he'd never do it as he saw first hand how his father's affairs affected his mother. So, I trust him completely.