Apparently Tom Baker was wondering why crushes never happened in the old series. Peter Davidson wasn't even allowed to put his arm around a female companion. It was all just hand holding. These days, it's always about "sexual tension".*shrugs*

Moffat said that Ten was the "Charmer", while Eleven was "Awkward". Twelve didn't want any of that "romance" stuff. Even if he got a tad jealous when River ignored him for another guy.

Donna had the right perspective and gave Ten what he needed and vice versa. I don't think Martha would have put up with Ten if she hadn't been infatuated with him. Luckily she was able to leave on her own terms.

Twelve and Bill was the closest to how it was in Old Who. She wasn't originally written as gay but Moffat changed it at the last moment.