Pft. And who is the plot to dictate anything? Time can be rewritten! Or not. But, shh. Let Donna believe in the Doctor and his foreverness. She had to believe in that.

"Enigmatic, secretish, and bossy. And what about Rose? I bet she bossed you around too. Is it a power thing? Do you like your human women to dominate you because you're a powerful Time Lord? Is it a kinky sex thing? Don't worry, you're secret is safe with me, Space Man!"