A little help with the movie Memento?

Dude, Has anyone ever seen Memento? have watched this movie AT LEAST seven times. I thought it was that Teddy helped Lenny kill his wife's killer, then when he realized that Lenny couldnt remember new things, Teddy had him kill drug dealers so Teddy could have their money. BUT. Someone said it was that Lenny made it all up, even Sammie, and that his wife really had diabetes and his memory problems made him believe he was looking for revenge. WTF? WHICH ONE IS IT?