Complex sentence: The song is about Goofy taking a girlfriend up in his plane, obviously on the ride of The Barnstormer at Goofy's Wiseacre Farm, however as he flew through his barn, and took her upside down and crashed into the watertower, she left him.
Split into simpler sentences: The song is about Goofy taking a girlfriend up in his plane, obviously on the ride of The Barnstormer at Goofy's Wiseacre Farm. However, because he flew through his barn, and took her upside down and crashed into the water tower, she left him.