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Nine wasn't really interested in such things, but he got a kiss from Jack non the less. Rose had no idea how to react to that.
Ten was quite the ladies man (even if he didn't always want to be), but after Rose the closest thing he got to a new love interest was the Master, leaving Martha and even Jack feeling overlooked. It was intentional on the writers' part, and they have no doubt what would have happened if the Master had indeed moved in with the Doctor in the TARDIS.
Eleven didn't discriminate in the kissing area, and Craig was ready to get snogged by the Doctor until he remembered he had a girlfriend.
The whole Doctor/Rory thing is mainly thanks to Matt Smith who for some reason put it upon himself to improvise the Doctor having a crush on Amy's husband. Several times he can be seen kissing and petting Rory, and one of his improvisations came too close to an actual love declaration and had to be cut out. In the comics is became apparent Amy didn't mind at all when she told them to kiss again "But slower". Rory was not a huge fan of the whole thing, but he eventually came around and kissed the Doctor on the cheek.
So as they say "The Doctor has been eleven different people. He doesn't fit neatly on the Kinsey scale"
"Well this is new."
If it does happen one day, poor doctor.