Ludwig van Beethoven, while a brilliant musician, was a very temperamental man. He had a very rough upbringing, with his father beating him on a daily basis for minor mistakes while learning to play several instruments.
Throughout his life, Beethoven was extremely shy and did not like his own physical appearance. He had friends, although the majority of them were male, with very few female friends. He was known to have a violent temper, and also suffered bouts of depression, and even went through some suicidal bouts as well.
The extreme pressure put on him by his father in his early years could have played a huge factor in his decision not to marry. As a young boy, he was often locked in the basement, without food, water or sleep, so that he could get extra hours of practice on instruments he was learning. Whether this helped to achieve the level of brilliance that we know, is not clear. His father did not have the genius for music that Beethoven himself held.