A passing thought

[tigerfort]

If I were (a) Steven Moffat and (b) feeling exceptionally cruel I would have the Doctor give River a parting kiss after their next adventure together. And have her as flatfooted by it that time as he was at the end of "Day of the Moon". Which would be very sneaky (though also cruel, especially to River as a character), setting her up for the heart-break we saw this time round without them ever having had a romantic relationship - she wasn't mourning its end, she was regretting that it will never happen....

Of course, I'm not Moffat, and he isn't always that evil to his characters. But it isn't unheard of.