What was my biggest mistake.

Ok, this is the first time I've asked for one of my games to be analysed... but I think this is a pretty good one... what was my biggest error?

Game 1909523

I think maybe my 5th move was the first mistake... but I don't think it was my biggest.

15. ... Na5 was the most fundamental, 44. ... Rc1 is in second place.

I think your biggest mistake was destroying your pawn structure like you did. There was nothing left to put in front of your king. And giving him the knight on move 15 was pretty bad too.

Ok, move 15... that kind of thing I need to watch more, and I need to work on preserving my pawn structure... thanks!

When I gave up my rook I think it was simply a lapse of judgement or something like that.

I have alot to learn, I'm still pretty much a beginner.