what happened to u in the first game, is what happens to me frequently.
at some point in the game i make an a bad exchange, and end up down a valuable piece.
for example in your first game, early move 6.e4...dxe4, 7.Bxe4...Bxe4, 8.Re1...(here u had no way of taking back a piece. u could only threaten the black bishop on e4, thus u are now playing minus one bishop.)
i also need to improve on this.
a humble opinion.
...and I have no idea why!