The opening I played is the Sicilian. I don't think this particular line is theory since I have never seen a queen side fianchetto from white in any of these lines so it's probably a bad idea to do something like that.
This opening can be played in a few ways but in general it's good because it allows dynamic play from black.
I must say that I don't think you really understand how strong 13. Nh4 is, it's just that you didn't see the right idea. I think you should have played Nh4-g3-Ng2-f4 and generate activity, I was sure this was the plan during the game and quite surprised when you didn't play this since otherwise the knight was just bad on the rim.
Probably 13. d3 was better to allow Bc1, stopping Bh6, you definitely do not want to allow black to get in Bh6.
I didn't play 13.... g6 just to stop use of f5, it's also to prepare Bh6 as already mentioned and Nh5-Ng7 to allow for a pawn push to f5.
I think you have a serious positional problem if you think Bxc1 was okay to allow, because it was not! You should definitely had held onto your good bishop, my bishop was terrible, at least your darksquared bishop had some activity, especially if you had put it on e3 to stop Bh6 and guard d4. Exchanging those bishops is what black wants to do in that position.
25... Kg7 isn't a nice move, it wastes time. It's probably the best waiting move black can play, but being objective is important, probably f5 was better.
The Ng4 and f4 move from you made no sense to me.
Your side variation is faulty unless I'm mistaken, the bishop on a8 is hanging. Besides after Qe4 black should play Rxf4 with a winning endgame.
Also, give yourself some credit, don't write axb4 as if it was no big deal. It's very important black doesn't get to castle queenside and double rooks on the f-file and you also remove your passive rook!
This was just my initial thoughts and remember to check your ideas with a computer! Have a nice day :)
A game versus Simasun. I know hes a player that checks out every possibility and still didnt check somethings not right. A couple huge blind spots (playing to quick and/or while at work). But his opening was nice. Aside from the pawn that I left hanging (but he didnt take for positional reasons -I think he could!) he had me pushed back pretty quick.
Id be glad to hear a bit about the opening he played. Why is it good to play against 1. e4? How could I have prevented that wall of pawns that prevented my pieces from moving?