The Doctor is more involved in the lives of Amy and Rory than he ever expected to be [as of A Good Man Goes to War]. He met a seven-year-old girl, and now discovers that it’s possible, at some future point, he’s dating their daughter. ‘They’ve got a baby…and look who it is!’ I mean, he must wonder if he can cross the TARDIS control room without Rory punching him for practice.
It’s everything the Doctor has ever tried to avoid–this man who avoids any kind of commitment, any kind of relationship–and he’s practically got a family unit around him, as dysfunctional as it is. He can’t just walk away. That’s his plan, however much he loves them–to hang out with Amy and Rory for a few years before they grow up too much, and then bugger off before he screws anything to permanently. Well, he can’t this time. He absolutely can’t. He’s committed. So it’s complex. It has to be. That’s the only way to write relationships. They do get more complex–every relationship in the world. I like that. I like the Doctor tripping over the consequences of being him.
Steven Moffat on 11′s relationship with the Ponds (Amy, Rory, River) from DWM 438 (August 2011)