He wasn't paranoid yet, but his old hearts were fairly hardened these days. As much as he always told himself that he wouldn't let himself get attacked, that he wouldn't drawn in by another and grow attached, he did it time and again. Some just hurt more than others. Grumpy was pretty much his middle name lately. Yes, too much like Sarah Jane now. Though he could blame himself for most of it. If he hadn't had dropped her off, she might still be with him or she could have met Rose's fate, which may have been worse to him than her being mad at him for years and disappointed he'd never returned.
"I am quite particular in who I 'mess' with as you coined it. You don't see me sleeping around with just any old thing. Not that my head is easily turned anymore either. Those days are gone." Which was true. He hadn't brought anyone into his TARDIS since she'd died. He just couldn't bare the loss again.