Think, people!

Okay, the question has been asked over and over again:

"Why didn't the Doctor stay in the parallel world with Rose?"

The answer is simple and not nearly as psychologically convoluted as people are making it out to be. And the answer is: He couldn't. He literally could not stay there. They only had a few minutes to get Rose back to her world and leave again before the walls between realities closed up again forever, AND he had to get Donna back home. He had to get Donna back to her home, so she could live her life after he wiped her memory.

Exactly how was he going to manage to do all that while fulfilling his fantasy of being with Rose again? It would have been a horribly selfish move to leave Donna's head burning up from the inside out while he went gallivanting around with Rose. He also couldn't wipe her mind and leave her all on her own in the parallel world either because she'd be left with nobody and no memories of what happened to her, and it's not like the Doctor could stay around her, because the memories would come back and she'd burn.

So, really, the answer is simple. He didn't because he couldn't. He has a greater responsibility to others than to his manly urges.