More computer analysis I do not understand ...

White has just taken Black's pawn and as you can see by the move list, I - playing as Black - then moved Nxf4.

But the computer analysis says this is a Blunder.

While I accept it might not be the best move and might even be an Inaccuracy, I'm having a hard time accepting it as a Blunder.  The move the computer says is Black's Best Move from this position is Qh4.  But I don't see why.

White has two responses, either put the King on either g1 or g2 from which I can put him in Check again and he just moves away again.

My thinking with Nxf4 is to threaten Qg2 mate on my next move, not something he can simply move away from like a Qh4 move seems to allow.

So why is Nxf4 a Blunder when it threatens Mate and why is Qh4 the Best Move?

That's why you need coach my friend, coaches can tell you exact reason why engine is telling that move. If you just work with engine yes you will know the best move, but you will not understand why is that a best move.

If you take with the knight, white can play rxn sacrificing some material to end your attack.  qh3, kg1, ng3 threatens qh1 checkmate.  Not sure how white prevents that since qf3 looks terrible.  

Thats my quick take -- you neglected to consider white sacrificing a bit of material.  White does have an extra piece, and might have some shot with the sac.  Certainly he isn't getting mated or losing material right away.