This achievement occurs during Episode 4 - Double Visions
Once you're finished doing what you need to do in Emmett's lab do the following:
• Interact with Exit.
• Interact with Emmett.
• Dialog (Emmett): "You Can't Marry Edna!"
• Dialog (Emmett): "You're too young!"
• Dialog (Emmett): "You're supposed to marry someone else!"
Credit to T_l_M_B_0 of PST