* To show the man Danny was before he met Michelle, the "regular Romeo" Ray was referring to on the wedding day, a man for whom one-night stands were not unusual occurrences (i.e. he was not a priest), hence the nonchalance on the surface. The re-appearance of the leather-jacket the first time he thought Michelle had betrayed him foreshadowed a Danny reverting to his old ways.
* To show that he is also no longer the man he is willing himself to go back to, a man who didn't know what being in love was, the pre-Michelle Danny in short. That Danny couldn't bring himself to kiss Drew goodbye (when they just had sex) and ended up tapping her on the head is an illustration of how genuine gestures of affection and tenderness are now only reserved for the woman he loves. (He was always touchy-feely with Michelle pre-betrayal.) That tap on the head was worse than nothing. You tap dogs or children on the head, you wouldn't tap the person you just had sex with if you cared about him/her.
* To show the difference between meaningless sex and making love, to highlight what he has shared with Michelle. Even though they never never went all the way, Danny made love to Michelle not just with his body, but also words (in her room at the Bauers before the wedding, on their wedding night while giving her backrubs), looks (too many to list), infinite tenderness (even during the love scenes after their fight at Ray's church, asking Michelle whether she was okay before unbuttoning her blouse) ... he bared his heart and soul and dreams to Michelle. With Drew, he didn't offer anything other than casual sex. Actually, he didn't offer anything period. He just used her, and vice versa. He gave her nothing, at least nothing meaningful.
* To show that Danny could sleep with a Drew every night and it still wouldn't diminish his love for Michelle, which he never denied by the way, or help him forget her, how hurtful her betrayal was. Otherwise, why would he show up at her doorsteps right after the act?
* To put an end to martyrized Danny, make him human (he too can make mistakes -- stupid, foolish mistakes) and balance the scale (more or less) in his relationship with Michelle. He may feign nonchalance in front of Drew but I don't think we're going to see him mention this to Michelle today, which a man feeling no remorse could do casually. If he does to get a reaction out of her, it means that he wants to hurt her, which means that he cares what she thinks. If he doesn't, it means that he's feeling guilty or thinks she wouldn't care if he did or did not.
* To show that Drew could not presume to "know" Danny, grasp who Danny is, just because they had sex. ("Don't try to turn my life into something it isn't.")
And where Drew's concerned? Well, I'm not sure if this is what the writers intended but it's mostly what I've got:
* It showed that Drew still has a long way to go before she can overcome her inferiority complex towards Michelle, become a person who no longer defines herself in relation to Michelle. She can't go on blaming Michelle or Selena or Jesse every time something bad happens to her. It's high time she grows up. This "poor me, life's unfair" routine is really getting old.
kristi