It's stupid! In the "Parting of the Ways", Jack gets exterminated and Rose resurrects him. Right after that, Rose passes off the Time Vortex to the Doctor who then, um, dies. Rose doesn't remember and the Doctor's regenerating. SO I always assumed that neither of them realized that Jack was alive again and left before he could catch up. But in "Utopia" RTD makes the Doctor say that he abandoned Jack. Which is plain fucking stupid and a HUGE fandom peeve for me, if you hadn't noticed :P

Don't be ashamed, we need normal people too, not just pervs.