You shouldn't have sex with your partner's family members.
Matt talks to his husband's cousin, Gregory, and finds him really interesting.
Matt wants to spend more time with Gregory.
Matt meets Gregory at the coffee shop to chat over breakfast.
Matt invites Gregory over while his husband is at work and the two end up in bed together.
Matt and Gregory develop a friendship which brings Gregory and his cousin closer together.
Gregory feels incredibly guilty, and skips family gatherings for years to avoid running into his cousin.