"We should really have had this conversation before this point," the Doctor theorizes. "And we still should, if we're going to, well, be----"

Be what? A couple? The Doctor couldn't even keep himself still for five minutes, much less be able to sustain anything resembling a relationship with anyone. And there were things he had to work out (his attraction to Morgana, for one, something he should probably talk to Rose about at some point. Or possibly take to his grave, one or the other.)