"Sean: My wife used to fart when she was nervous. She had all sorts of wonderful little idiosyncrasies. She used to fart in her sleep. (...) One night it was so loud it woke the dog up. She woke up and went ‘ah was that you?’ And I didn’t have the heart to tell her.
Will: She woke herself up?
Sean: Ah...! But, she’s been dead for 2 years, and that's the shit I remember: wonderful stuff, you know? Little things like that. Those are the things I miss the most. The little idiosyncrasies that only I know about: that's what made her my wife. Oh she had the goods on me too, she knew all my little peccadilloes. People call these things imperfections, but there not. Ah, that's the good stuff."
- Good Will Hunting (Gus Van Sant, 1997)
At first, everything's "perfect". The people involved try hard to be nice and polite as they expect to build a healthy relationship. But some time later, usually both of you feel the "barriers of politeness" slowly fall down.
Long story short: when magic ends, farting begins. Under the covers, or while taking a shower with the other person. Pre-meditated or just casual rippers. And you both end up laughing about the sounds and smell.
Also there's hair, everywhere. And burping. Oh, and going to the bathroom with open doors while you go on with a conversation becomes acceptable. When seeing your significant other naked around your place doesn't mean you have to mate like bunnies all the time, it's the sign that you got to that superior stage and you somehow get used to it and you feel comfortable with those little details.
Being in a comitted relationship means several things, but the most tangible is the high level bonds of trust reach in every aspect, the intimacy goes from bedroom matters to the little trivialities that daily coexistence brings to the surface. That hairy, navel-lint-covered surface.