It really depends on a number of things.

If you're just using whoever you're having sex with at the moment at their own expense then you're a cunt. If they understand that it's nothing more than just some sexual fun between the two of you then that's ok, provided you're not aware that they're doing it for some fucked up emotional reasons under the hope it will become more. The latter sounds likely in this case.

Don't emotionally abuse people for your own physical pleasure.