1) Even more than his other selves, the Fourth Doctor is prone to getting distracted by shiny objects. I can't imagine getting through dinner or a movie without his running off to save the planet.

2) At various times, he travels around with Sarah Jane Smith, Leela and two Romanas. Regardless of whether he has any romantic intentions toward any of them, that's some awfully intimidating competition for his attention.

3) If we broke up, he would be bound to give me a K-9 unit, and I am just not a dog person. Not even robotic tin dogs.