Sameth on Feb. 15, 2013
For you non-Whovians, Rose Tyler was 9's Companion during his entire run and 10's during his first season. She fell for him during 9's run and he started to fall for her before his regeneration. Once 10 rolled around, the attraction seemed to grow...maybe because of pretty boy David Tennant. (Yes, I'm calling Rose shallow.)
Something happens to her (without going into any spoilers) and he kind of pined after her for the following two seasons that 10 remained on the show.