Da Vinci's personal life was never talked much about. He had many friends that consisted of mostly men of all areas of politics, art, and math. His only female friend was Isabella d'Este Louvre who was a major political figure and a leading woman of the Italian Renaissance era. She lived in Mantua and Da Vinci had drawn a portrait of Louvre in 1500 during a journey that took him through Mantua.
Among his many male friends were mathematician Luca Pacidi. He and Da Vinci worked on a book together in 1490. Niccolo Machiavelli was especially close with Da Vinci. They remained very close friends. Machiavelli was an Italian Diplomat and political philosopher along with being a poet and musician. Da Vinci apparently had an interest in those that were had power and were very artistic. He was a curious man that led to be friends with others that were just as curious about him.
Franchinus Gaffuruius was a music composer during the Renaissance era (1400-1600) who also became friends with Da Vinci. Leonardo chose to remain very quiet about his relationships with men and several times he was accused of sodomy with young boys of age 15 or 16. There was never enough evidence however to say for certain if this really happened.
In 1506 there was a 15 year-old by the name of Francesco Melzi who was the son of a Lombard aristocrat. Melzi was a student of Da Vinci's, but it was suspected that it was more than that through a letter he confessed his love for the boy. Gian Giacomo Capriotti da Oreno was another young male that became one of Da Vinci's pupils. He was nicknamed Salai. Eventually he and Melzi traveled with Da Vinci as they continued to learn the master's art. These relationships followed a pattern that Da Vinci had. It seemed as though the young men always wanted to learn art from the best.
Leonardo Da Vinci's homosexuality has never been a main topic of discussion when his name was mentioned. No one thinks about how many men he built a relationship with or how many pupils he slept with. It has never been a major issue simply due to his contributions to the art world. The fact that he remained quiet about his preferences also made reason of why we don't usually discuss his personal life.