This is a conversation Eric the roommate and I find ourselves having quite often (he's straight, btw's.) However, it always boils down to what do we define as "sex."
For the straight world (most straights I talk to tend to agree,) sex is going all the way; while for me, sex is any form of getting off from light stuff to the whole enchilada. I suppose there is no answer, like Savage points out. But I do feel as though the difference between a healthy amount of partners and an unhealthy amount all comes down to the way you feel about yourself, your partner and how the choices you made make you feel in the end.