I do envy Donna for: having no memory of that desperate, awful kiss on the beach between a broken teenager and a blow-up doll

I'm not sure if I agree with that or not. Yes, she's abandoned by *her* Doctor (*the* Doctor) but the alt Doctor has all of his memories and all of his feelings (he wouldn't have finished the sentence to Rose if he didn't). And it was proved/shown that *the* Doctor really loves Rose ("Does it really need saying?") but realises that here's a chance for Rose to be happy because there's a version of him which does love her and which can stay with her forever. In the Confidential episode afterwards, it mentioned that they both love Rose but that because *the* Doctor isn't human in any way that he can't stay with her forever and it's fairer, in his eyes, to give her a life with the Doctor even if it's not actually him. If that makes sense...