oh it's most definitely allowed but it is hardly ever the case. to be frank with you, a guy will almost always think he is the one using you, and you could very well convince you subconsciously that it's true.
unless he is madly in love with you and you dont care for him and you will leave the moment you have your panties back on, then it will almost always be considered you're the one being used. it's just the way it works.
i've used ppl and they were well aware that they were being used, but a guy just doesn't say no to sex...so is he even capable of being used? i "used" a guy i knew had lots of feelings for me..he was an ex...i just didnt give a shit i wanted some...so i got some...he knew he was being 'used' yet he still let me use him...so i guess technically he wasnt used. see what i mean? it's a paradox.