It had seemed like such a good idea at the time.
At first I was afraid, I was petrified...
He'd been in the neighborhood anyway, after all, and he was sure that Martha and Donna would love Sarah Jane, so what was the harm, really?
Kept thinking I could never live without you by my side...
And, yeah, Martha and Donna and Sarah Jane had got on fabulously! Very fabulously! Possibly too fabulously, actually, in the Doctor's esteemed opinion.
Which, of course, no one seemed to esteem at the moment except himself. He was, truth be told, beginning to feel just the tiniest bit left out.
But then I spent so many nights thinking how you did me wrong...
But when Luke had asked to spend the night at Clyde's (he wondered about those two sometimes, he really did) and Martha had suggested a karaoke bar for Sarah Jane's night free, it had seemed like such a great idea! Such a fun idea!
And I grew strong! And I learned how to get along!
Somehow, though, he'd ended up stuck in a corner watching Martha and Donna and Sarah Jane dancing around on a stage together singing at the tops of their lungs while getting progressively drunker, and for some reason they seemed to be stuck on this one particular song. The Doctor could not, for the life of him, figure out why.
But now you're back! From outer space! I just walked in to find you here with that sad look upon your face! I should've changed that stupid lock, I should've made you leave your key, if I had known for just one second you'd be back to bother me!
They'd sung it eight times now, and every time they'd laughed even harder than the last. At this point, they were basically standing on stage yelling it, clinging to each other in a vain attempt to keep upright, and laughing fit to burst.
The Doctor was beginning to think there was maybe a joke in there somewhere that he just wasn't getting somehow.