Here is an excerpt from an article I found:
http://www.berkeleyrep.org/HTML/SchoolOfTheatre/matguide_NB. html
He traveled his own path to fame
Regina Hackett, Seattle Post-Intelligencer Art Critic
"Was Leonardo gay? Almost certainly yes. Instead of marrying and having children, he had a lifetime male companion, one of the few people mentioned by name in his will.
Besides, the practice of sodomy was so widespread in 15th-century Florence that the Germans referred to all homosexuals as Florentines. Leonardo and his circle were accused of homosexuality, but the charge had little or no influence on his career.
A major bar to his advancement (and blessing in disguise) was not his sexual orientation but his birth status, the fact that his parents weren't married to each other. For this reason, he was not able to pursue university studies, where he would have learned to seek knowledge in approved texts, looking backward, not forward."