Lindsay Lohan went off the rails again after learning her on/off girlfriend Samantha Ronson had jetted to Nicole Richie‘s bachelorette party in Cabo, according to kik ster.com. Richie is rumored to be marrying rocker Joel Madden, the father of her two children. Lohan “went crazy” trying to find out who was with Sam on the Mexican trip because she “couldn’t get permission to leave the country . . . and wasn’t in vited.” Sources said that while Lohan and Ronson are not a cou ple any more, Lilo is still obses sive and “kept trying to track down Sam.” A rep for Lohan didn’t get back to us.