Some people banter about the term "nymphomanic" (or just "nympho" for short) when they really really REALLY like sex, but nymphomania (or "Hypersexuality (http://en.wikipedia.org/wiki/Nymphomania)" as it's now called) is a (debated) psyhological disorder wherein those who have it do need sex like a drug, but as with drug addiction, get to a point where it's not enjoyable (there's no more high) and need it just to feel "normal" again. (Sexual addiction (http://en.wikipedia.org/wiki/Sexual_addiction) is different, but related.)

I can't say if your boyfriend's a nymphomanic, of course. He may just have a very strong sex drive (I know my husband's is stronger than mine lately), but if it's that worrysome to you, try talking to him about it.