According to the pilot, he and his passenger had flown for approximately 1.5 hours prior to returning to his airport for landing. Prior to landing, the pilot became distracted by other aircraft within the vicinity of the airport and "[the pilot] forgot to switch to 'both' [tanks] on the fuel selector." During the landing, the airplane bounced and the pilot executed a go-around in order to perform "a better landing." While executing a go-around, the engine lost power. The pilot attempted to land on the remaining runway; however, the airplane touched down in a field and the left main landing gear collapsed. The pilot reported that he forgot to switch fuel tanks during the flight and that was the reason the engine lost power. Examination of the airplane revealed the left main wing spar was bent.