I'm female, and I've had sex on ketamine. I *can* feel sexual on it, then again I am a very sexual person...I would not describe ketamine as a 'sexual' drug ( I consider GHB and amphetamines sexual, for the record).
Sex on ketamine is very strange, becuase of course you are dissociated from your body. I did not have a bad experience on it (and I was able to orgasm, while tripping), but I think with higher doses, I would prefer not to have sex and just enjoy the trip. With low doses, though, ketamine is more recreational/less anti-social, and sex can be interesting, as it always is on drugs...
One last thing I will add: People get weird emotionally on ketamine, especially boys, so sometimes being with a love interest/significant other while on ketamine can be frustrating, becuase the other person will be emotionally distant which can be hurtful if you are sensitive...Having been involved with two ketamine addicts/dealers I can attest to this...it's not fun to be ignored by these men when they are k-holing!