The more I think about it, the more I think the tenth Doctor is demisexual. You put him in a romantic situation with Rose, and he’s generally up for it.
"This is my Rose. I want to smooch and cuddle her, because she is my Rose."
Anybody who isn’t Rose hits on him, and he gets confused and flustered. “Why do you find me attractive? You’re not my Rose. Stop finding me attractive. I’m scared.”