He first met Ashley, they made a pact not to date in high school, but that quickly dissolved. Later, he set Ashley up on a surprise blind date with his cousin, Grant, who he sent to Ashley's house to deliver her pizza. At present, he seems to be dating Peter, for when Grant mentioned to Griffin about potentially ignoring Ashley in favor of Peter, Griffin denied it. It also points to Griffin dating Peter because Ashley tells Griffin to tell Peter to say hello. Even though Griffin is experienced sexually, his boyfriend Peter is not. Peter states that he is not ready for sex the night he has a sleepover with Griffin and Haley.
Although it's unclear whether Carrie Costigan or Vic Volberg is Griffin's aunt or uncle by blood, it's likely that Carrie might be his biological aunt and Vic his uncle by marriage, since Vic does not have a "G" name as per the tradition of male names in his family.
After the episode I Do and I Don't, Griffin was never seen again after that, so what happened to him is unknown. Griffin is played by Brando Eaton.