*SPOILERS* movie makes no sense!

So he kills a dude in self defense, and I understand that the cops wouldn't believe him about that, but he drags the dude into the backyard in a carpet and kicks a little bit of leaves on his face. He runs in and throws his clothes in the trash right by the sink, while his undershirt is still quite bloody. Ok i get that he was having a bee attack and didn't have much time, but i watch a lot of CSI and this seems very very unlikely. OK it's just a movie, i'll give it that and end that note. Then what exactly happens to Otis? Why doesn't he answer the phone? The (unplugged) jukebox plays when he calls. Are we to assume that he was killed? Or just not answering the phone? And why the HELL would you go to some chick's house pretending to be your dead ex-girlfriend? You know she's dead.. wouldn't u think that this girl is trying to get something from you, even if u have nothing? OK let's just say he was curious to see this girl faking her way as his dead ex.. and he realizes she is effing nuts. He left and came back! What did the postcard say that made him go back? Noone knows and that is weird! The last one i have is the cab driver that knows Don but doesn't explain anything.. maybe that was just a creepy element but made no sense at the end.. anyone with some ideas please help me!