What is it about sex?

Spending a day NOT having sex has it's good points and it's bad.  Good:  We know we can enjoy each other without having sex and when you finally do have sex together it's phenomenal (hopefully).  Bad: you start to worry that all that silence between the two of you is sign of something horrible going on in the relationship.  Now we haven't had sex yet since Monday; except for Tuesday, we haven't even been around each other (I needed to crash from exhaustion yesterday).  Today at work, when I see him I really just want to tear his clothes off and just FORGET that we are at work and other people may happen upon our happy reunion.  I mean full-on sex; the thought itself makes me wet with need.  It's really too bad that he has to take his cat to the vet this morning.  It would have been one of those days.

So what is it about sex in a relationship that makes it a forefront object of said relationship?  If it's great, you feel really good and you want to see him/her again.  For MORE.  And then you progress onto actually building a relationship together, in between the rounds of great sex.  But the basis of the whole thing is ... sex.  Maybe there is something to the idea that having sex in a relationship just ends up ruining it.  Then again, if something is wrong in the relationship it can be seen in the physical part as well, or the relationship is just bad to begin with, like my last relationship.  Sex was great, but dude was a terrible human being.  All in all, sex is great as long as it is safe, but I gotta try to build a great relationship along side of the great sex.