I do and I agree with you, he is.
To Sage: Leave her alone. Forget you know her in any capacity other than as an aquaintance of your friend's. Don't spend time alone with her.
I do believe men and women can be friends in a capacity outside of a relationship, but honestly the friendship between and a woman is very different than one between two heterosexual men. In a relationship between a man and a woman, its not unusual for their to be sex involved at some point.
Why deny your sexual instincts? Higher-level brain function overrides a lot of instinct that man has developed (ex: thalmus and bladder-control), but you will never forget that instinct. Do yourself a favor and get out of this affair before you do anything stupid. A 30 minute fuck is not worth the insurmountable issues that will arise because of it.