Welcome. :-)

thx for help

Rxd2 would be a good option. If Qxd2 the bishop might get ur g pawn. Instead of 15. Na4 which doesn't seem to do much to him. 15.f4 which chases the queen and gives u more fun at using ur pawns to gain space on the board. More space on more you control the better your position usually is.

What should I have done? Rd2 or Qd2?

18...Na4 19.Qd3??...Qxb2# Short i know but still painful. Your pawn h4 was a bad choice to as it didn't solve the problem u had against your king.

what combo?

You lost this game because you missed that check mate combo, not because of 1.Nf3

So i guess a lesson for you here would be to make sure and check to see if your opponent has any checkmates before u move a piece. Especially when your opponents pieces are attacking at your king.

Interesting game though. You have some good play there in some parts and i hope you continue to learn and get better.