Here is a match I lost last night that I had been doing okay in, but my middle and end game ruined it (and my start wasn't very strong either):

I looked at your game from Feb.8 and thought I'd give you some pointers:

7.0-0 ? Castling is a mistake at this point. Black's last move, 6...d5 set up the threat 7...d4, forking the White knight and bishop, winning a piece. You needed to play 7.exd5 here to eliminate this threat. This fork remains possible for several moves but luckily Black never saw it.

11.Nb5? Your knight on e5 is hanging and can be captured by the Black queen. Your move, attacking the black queen almost forces Black to capture your knight. Luckily Black didn't see it.

15.Qa6? Sadly you missed a mate in two here. 15.Qa7+! Kc8 16.Qa8#. At the very least you could've also simply taken Black's knight on a2 with your queen.

16.Bxb6? Here you missed a mate in one. 16.Nxc6#

17.Qa5? Your knight on b5 is attacked by a pawn, so moving your queen just leaves it up for grabs. Better was to continue the attack with 17.Nxc6+, if then 17...Qxc6 it's mate in two 18.Ba7+ Ka8 19.Qxc6#. Also better would have been trading queens with 17.Qxb7+ Kxb7 and then taking his rook with 18.Bxd8

18.Qxb5? Better would have been to win the black rook with 18.Bxd8. Up until now you were winning, but now the tide is beginning to turn.

20.Nxf7?  Trying to fork the two black rooks. You should have taken the Black knight on a2 with your queen instead. Now you're losing.

21.d4? The Black knight on a2 is still up for grabs! 21.Qxa2 should've been played.

22...Qxb2?? Your opponent commits a fatal blunder with this pawn grab. His queen and king are on the same open file. You can now skewer them with 23.Rb3, winning the queen. Sadly you missed it.

I will stop the analysis at this point. The rest of the game no longer presented you with any opportunities to save the game.

This is hardly an in-depth analysis of your game, I merely pointed out the most obvious tactics. I would recommend you look at this game again and again until everything I pointed out to you pops right out at you.