There have been teases of a love interest for The Doctor in the past, but it was never full fleshed out. He came close to telling Rose that he loved her and he even got married to River Song, but the closest he ever came to having a companion that was more than a friend was in the 1996 made-for-TV movie, and many fans of the show would like to forget that ever happened.Fox Studios had a big hand in making the eighth Doctor appear to fall in love because they thought American audiences wouldn't accept a lead male not falling for his leading lady. but that's probably what happens when us Yanks try to take something British and turn it into our own thing. Apologies about that. Every protagonist on every show seems to fall in love with someone these days, so it's refreshing to have a character who chooses to keep a degree of distance from the idea of love. A girlfriend would certainly limit his ability to make decisions for the good of everyone else at the expense of someone he cares about, which has happened on numerous occasions in the show's history. He just works better as a bachelor.