Moahout is right.
You shoud have stopped developing for a moment and dealt with
the threat to the Bishop. Allowing it to be exchanged on f4 pulled the e3
pawn onto f4 and weakened your d-pawn.
Black cashed in on this weak square.
Mahout's Bg5 is a good alternative.
Pulling the Bishop back to g3 is also an idea.
d4 is still solid and if Black chops the Bishop you have an open h-file
to drum up chances v the Black King.
Having said that and looking at the postion from a player who plays the Black
side of this opening I know Black does not have much to fear.
I Liked Black's play.
In this postion he could has nicked the d-pawn. (...Bxd4)
But Black played 9...Nc6 instead - getting a piece to d4 was more important than
the pawn. And if you saved the pawn with 10.d5 then Black uses that pawn
to play a timed e6/c6 and opens up the game.