Why can't my king capture rook

I allowed rook to capture a knight thinking I could capture his rook with my king since my rook had his knight pinned to his king. Is there a rule I don't know about?

Got into this position in a game. White to play.

I liked this win, I think I am improving slowly

Why does chess.com call this a draw when you could technically still mate in this position

Help me spot the mate that I missed during the game

I made it actually funny rule

R(ule)eal

Get ruled on

Rule

eluR

(Sonic fans do not) rule