Here are my guesses.
1.) Andy is gay and made a pass at Brian.
Alternate 1.) Brian actually had an affair with Andy.
2.) Andy made a pass at Melinda.
Alternate 2.) Melinda actually had an affair with Andy.
3.) Andy is now becoming a woman.
4.) Andy somehow insulted Melinda by doing something or other.
5.) Andy now actually IS Brian Wilson, thanks to extensive plastic surgery. The old Brian lives in a Hollywood retirement home, is 500 pounds and the happiest he's ever been thanks to the all-birthday cake diet.
6.) The Wondermints ritually slaughtered Andy at one of the band getaways.
Alternate 6.) Andy wanted to ritually slaughter the Wondermints.
7.) Andy was unmasked as an agent for Phil Spector, who really WAS interested in stealing Brian's ideas for his upcoming sessions with Starsailor.
8.) Andy Paley is a dick.
Alternate 7.) Brian / Melinda / Darian / Jeff is a dick.
Nope.