here's a description on episodes that hasn't air yet:
All About My Brother 5/5
Georgina informs Serena that she can reveal a deep dark secret from Serena's past, but no one is prepared for what Georgina does next. Blair and Jenny's power struggle continues when each of them start spreading scandalous rumors about each other on Gossip Girl. Dan sees Jenny's new beau, Asher, cheating on her, but Jenny doesn't believe him. Rufus goes to Lily for advice on how to handle Jenny's new behavior. Serena tries to confront Georgina, but she leaves before Serena has a chance. After this Serena says that she and Georgina are not friends.
Woman on the Verge 5/12
After Georgina reveals the true reason Serena left Manhattan, Serena goes back into her old habits. Her friends Blair, Nate and Chuck in order to help her, have to put their differences aside. Unfortunately, Serena is too ashamed to share the truth with Dan, therefore he assumes the worse about his girlfriend.
Meanwhile, Rufus is excited when his band is invited to perform at a Rolling Stone-sponsored concert, but Lily is the last person on earth he expects to see at the performance, especially since her wedding rehearsal dinner is the same night.
Much 'I Do' About Nothing 5/19
An unexpected guest shows up at Lily and Bart's wedding. Georgina goes somewhere where she can do no harm. Dan and Serena try to work out their relationship after Dan cheated on her. Blair plans to go somewhere with Chuck.
Wow, I can't believe Dan cheated on Serena. He's not the type of guy who cheats on his girlfriend.