How does your mind plays against itself?

I tried to learn the ruy lopez opening and all its variations and defence after my lose against someone using ruy lopez in an otb game. I saw this one variation on the net and I tried to challenge myself. I played using this opening and defend against it after seeing many GM's games. Here it goes:

After analysing it bit by bit, I saw black has a big win:

So, it doesn't hurt to analyse before making any moves.