I wouldn't mind if Clarke stays single. It would be a bittersweet ending to have her (in the final moments of the series finale) looking up at the stars alone and saying "May we meet again" in Trig, thinking of Lexa and maybe everyone else she lost, too, but mainly Lexa. No Boris. No Octagon. Just her. It would be even sweeter if the stars happened to be in the shape of the thing Lexa wore on her forehead (showing her Heda status) or Trikru's symbol or the Coalition's symbol.

But if Clarke does move on, I'd rather her with Niylah than Boris, which is where the writers seem to be going