Drake started the blowout NYC nightclub brawl last summer with Chris Brown ... by sending Brown a handwritten note that read "I'm f***ing the love of your life" -- this according to Chris Brown's bodyguard.
According to the lawsuit, obtained by the NY Daily News, Patrick Strickland -- whose head was badly bloodied during the flying bottle attacks -- is suing Drake and W.i.P. nightclub, where the brawl took place last June.
Strickland says Drake's note -- a clear reference to Rihanna -- started a verbal altercation, which then led to the all-out melee in which several people were badly injured ... including Strickland and several other clubgoers.
According to Strickland, the club is also responsible for over-serving Dreezy -- and seating him way too close to Chris ... in light of their public beef over RiRi.
He's suing for unspecified damages.