I'd say it depends on where your tolerance is at and how habitual a user you are, etc... I find that for those who only use it occasionally it is a strong aphrodisiac... but if you're a regular user and are adjusted to it, and find yoursef a bit over-saturated with THC at the time, it can numb you out a little emotionally and physically and create a bit of dissociation which can take away from intimacy to some degree.
As Morgan said above, depends on the person as well... depends on where you're 'at' and what sexuality means to you, what you tend to want to get out of it, et cetera. Orgasms are a fleeting moment... and I find that I'm more apt to chase down that moment when high; while I am more apt to enjoy each moment leading up to it as well when not.