As stated previously, Clara lied to the Doctor by claiming that Danny was alive and well. She didn't tell him that she really was alone but instead let him go on his way to return to his own home - something he'd been awaiting for hundreds of years. In Clara's mind, it would be selfish to keep her best friend all to herself at such an important time in his life but when the Doctor found out that Clara was in trouble, he immediately raced to go help her out. It's true what they say - if you really love someone, all you have to do is let them go and if they come back, it was truly meant to be. Perhaps this is Doctor Who's way of letting the fans know that the Doctor and Clara are meant to be, too.