Cousin had a boyfriend of 5 years nobody has met

[MPowering1]

Maybe he doesn't want to mingle with the family.
Maybe they're not serious enough for family involvement.
Maybe he's married and spends less time with her than you think.
Maybe she's gay and doesn't want people to know, so claims someone who is just a friend is a boyfriend.
Maybe she thinks she'll be hassled because he's Muslim.
Maybe he's heard about her family members who have an unhealthy obsession with other people's lives and he's avoiding that mess.

Pick one.

[Mongobongo]

Your cousin is 50 years old, she's not a 18 year old girl who doesn't know any better. Sle's grown woman and then some. What she has works for her. Let her live her life how she chooses and get on with your own.