Sex on ket (for a guy) CAN be good, if the dose is right, it will let you fuck for ages before you cum (great for her) as like FF said your cock is bit desensitized...
But a little too high of a dose you with really struggle to cum, keep it up/even get it up (bad for her)
Sex on ket for a girl (ime) is kinda marmite. Some girls don't like to be fucked on ket, and also struggle to cum. But I've met plenty of girls who like to do a massive line before you enter them, I think it can help them relax and 'let go', especially if they're a sub. Or they just love k-holing while getting fucked hard, 2 great things at once haha.
K sex is wicked imo. I've had so much. It's great because I would fuck for ages, not cum, make her cum, then when I want a break, just suggest more lines, because you are both k addicts and love drugs, both happy to stop, I've railed like 2g lines off tits before, had line of K done off my boner, licked it from her pussy (she said this made sex worse as it numbed her clit). But if I started to flop it was never ever the end of the game because a quick breather or a decent blowjob or some dirty talk would always bring it back up... Then go again. I've gone for hours, ending up with friction burns on my cock and all sorts lol
Man I'm horny, and craving k right now.