Ending 1: Link the fire: You pressed the cosmic reset button as everyone else has before you. Congrats, you didn't solve anything, but you didn't fuck things up either.
Ending 2: Let the fire die: You've had enough of this cyclical bullshit and have decided to let the universe die out. Too bad someone else will eventually just become a Lord of Cinder out of sheer willpower and start another age of fire (like Ludleth of Courland did) and fuck that up. You solve nothing. Gratz.
Endng 2b: Kill the firekeeper and steal the first flame: WHAT THE HELL IS WRONG WITH YOU? You're just being a greedy ass and/or a pussy who can't sleep without a night-light.
Ending 3: Usurper of Flame: Congratulations! By letting your fully grown dark sigil thing EAT the first flame or something, you have somehow frozen the cycle of light and dark and are now stuck in the twilight of undeath forever. On the plus side, everyone lives forever. On the downside, everyone looks like a corpse and has alzheimers. On the plus side, HAIL TO THE KING, BABY!