There were five reasons why Hermione Granger didn't date. Her parents, her female friends, even Ron and Harry had started to question her as to why she hadn't been in any sort of relationship since her failed attempt with Ron. She could normally get away by saying "I have my reasons", or any variation of the phrase, but she had started to get asked "why" in return. So one evening, she decided to attempt to compile a list of her reasons as to why she refused to date.
Reason One: She didn't have time. Between her job as a professor at Hogwarts and her part time service as a researcher for the Ministry, she had little time for a personal life. Harry and Ron were still her best friends, but Harry had married Ginny after the war was over, and Ron, being the international quidditch star, was with a new woman (or man) every week. She just hadn't the time to put into a healthy relationship.
Reason Two: She was getting too old for "dating". A thing about being young is that you go out, have a drink, and enjoy the company of complete strangers while getting tossed. A thing about being an adult is that you have responsibilities, jobs, and places you have to be at early hours in the morning. Since the war took up a majority of her youth, she never got to experience that stage of youthful dating and she was way too intelligent to waste her time now trying to pretend that she is ten years younger. At the age of 30, she was definitely too old to date.
Reason Three: She was very hard to get along with. She is bossy. Everyone knows that. And guys are often put off by her vast intelligence. That's not to say that she's conceited in any way, shape or form. She just happens to know where her flaws lie. Being very picky can also be a bad thing. In a man, she wants a caring, intelligent, sensitive, humorous person, which no man she has ever met has possessed all of those qualities. She'll meet those who are funny but as smart as a sack of potatoes. Most of the intelligent people she has met have had no sense of humor what so ever. And the sensitive ones have been either not interested in women, or spineless pansies that are afraid of even the silliest of things. No, she has deemed herself impossible to get along with and even more impossible to please.
Reason Four: Most of the good men were already taken. At her age, which she has already mentioned as quite old, most of her peers were already married with families. The men in whom she had daily interactions with were all unavailable. She had already mentioned that Harry was married and Ron had his assortment of flings, but even those she worked with, Neville, Dean, Seamus, and even Draco Malfoy, were all married (granted, some to each other). The point is, all the good men in England were taken, and she'd be damned if she was going to go to another country to find a single man.
Reason Five: She was in love with her best friend. Since the day she met him on the Hogwarts Express she has been in love with Harry. Sure, she attempted to date Ron, but he was never really the one she fancied. She felt it was what everyone expected her to do. That was the day she realized, really realized, that she was in love with Harry. During the war, her feelings grew, but there was nothing she could do, being as Harry was only fighting the war so he could return to Ginny. He was always fighting for Ginny, never for her. All he could ever talk about during those long years was how he wanted to marry Ginny when the war was over. Secretly, it had torn Hermione apart. But she could never let that show. She was the strong one, the brains behind the 'golden trio'. She couldn't afford to show trivial things like love or sorrow. There were more important things to think about, more important things to deal with then her love for her best friend. And that has how it remained for the rest of the war. She was the maid of honor at Harry's wedding; she was there the day his first son was born. First and foremost she was his best friend.
Reason Six (to tell people instead of reason five): She didn't need to date to be happy. If someone came along (which she doubted at her age), then great, if not, no big deal. She was content with her life.