Da Vinci might have been but I don't think there's any reliable and authoritative surviving evidence of him having any sexual dalliances of any sort. The biggest clue, to me, is that the modern homosexual movement doesn't offer any 'scholarly' evidence that he was one of them. I think that if he were, he also was entirely celebate.
As much as anything, I think the conflict between da Vinci and Buonarroti was their personalities were polar opposites. Da Vinci was charming, urbane, and a snappy dresser. Michelangelo was grumpy, stank, wore clothes until they rotted off him, and resented anything that took time away from his work (including eating, bathing and recruiting patrons).
There's not much middle ground there.
Michelangelo may have been clinically insane..........