Games I lost

You was crushed nicely

I have 2 misunderstandings

1. Why 13...Nf4 is so wrong... maybe because this allows 15. d5? I don't think so, there are and other moves after which white has the advantage (as the engine shows) basically I exchanged a knight for a bishop and positioned my queen in an active square. But my light bishop is still not developed. And why 13...Ne3 seams to be a better move? Basically I exchanged a the same knight for the same bishop, but now is my turn to move and I can develop my bishop, gaining a very important tempo?

2. 11...Nd5 is a wrong move? moving the knight second time, while the light bishop is still undeveloped?

1) Nf4 just concretely bad. You're not gaining a tempo, you lost it. After you take bishop Qxf4 white have g3(important move for attack your king in future) pushing your queen back.

2)Mb 11. Nd5 was premature. You must take care about development of your light bishop. Not to move your knight 2nd time with no concrete reason. Also you dont want to exchange it with this dark bishop which is not very useful peace for white in the moment.

A man who is willing to commit suicide has the initiative.

- Boris Spassky