Slacker and Steve - OPP - Her boyfriend wants to see other people…while they're still in a relationship 5/18 (Audio)

Erin (no, not our Erin) and her boyfriend have been together for a couple years. Previously, her boyfriend has joked about having a threesome, but it's gotten more serious. He's even asked her about having an open relationship. She doesn't really want one. Is it possible for him to have an open relationship if she doesn't want to be involved in one? What should Erin do?