2. Doctor Love
It's not true that the Doctor of the classic series did not fall in love. In the William Hartnell adventure, the Aztecs, the first Doctor quite clearly falls in love with Cameca, even if it is a subtle romance. After that, the Doctor's sexuality seemed to never quite be mentioned on the show, although if one looks hard enough, there are likely hints. Even the much vaunted "kiss" of the TV movie is more a moment of passion than it is one of romance. However, when David Tennant came onto the show as the Tenth Doctor, the romance element was dialed up to take advantage of the chemistry between Tennant and Billie Piper. The Doctor has been lusted after and has indeed lusted after others. While Smith pretended not to see sexuality in others, there was clearly a lot of flirtatiousness in his Doctor, particularly in the relationship between himself and River Song. This has been toned down for Capaldi, who is decidedly. "not your boyfriend". There has always been frank and obvious relationships between others on the show, including same sex couples and a misjudged attempt at sexual humour in the episode Love & Monsters. Some fans hate this new aspect to the show but it feels more real in many ways and a lot more grown up than merely pretending that love and, by extension, sex don't exist in the Doctor Who universe.