Game, where did i majorly blunder

I played this game at a chess club. Where did I seriously blunder?

I assume that you played white?  You seemed to get an equal endgame, and then misplay it.  Your rook remained passive, and your majority was never activated.  Just what I see.  didn't see a major blunder, more like an accumulation of smaller errors.  (Take all of this with about a pound of salt...)  You also might have missedsomething at move 29, instead of Rd3, perhaps Rh8 h6 Rh7 Rc7 with a sharp position?

White allowed Black to get two passed pawns that are next to each other and in the center. And the fact that Black's king and rook are in a very supporting position. There is no way White can tie this game. Additionally, after White's king moves to row #2, 42. ...Rc2+ wins the a-pawn.

I think the problem was that White sought trades too often, and because of his/her desperation to simplify the endgame, he/she overlooked Black's benefit. Tip for White: Think things through next time: not every trade is good.

Although I'm aware I don't qualify to criticize anybody's games but my own, I'll tell you what I wouldn't have done in your game: the first knights exchange (black recaptures with the other knight, maintaining his position with the simple removal of material from the board (doesn't seem to accomplish anything); White traded an amazing dark square bishop for a passive knight on the seventh rank (with that much space, I'm positive the bishop would be more valuable than the knight); and, finally, I would have tried to maneuver my rook in the endgame to a more active position (as tazerdadog said).

I like White's position by move 15, with the knight on f3 and both DSB and queen eyeing the castled king, I would probably try to launch an attack instead of harrass the enemy queen on the other side of the board. Maybe a good player will provide you with more specific and direct advice.

You were golden to move 26, where you would have been much better off starting your majority assault and definitely not concerning yourself with trading down.

I think just the endgame went wrong for you.