You are picking up your to-go order from Texas Roadhouse. While you are waiting, you see your favorite cousin's significant other sitting at the table with a woman you do not know.
What's your next move????
Me personally, I've been conditioned to mind my own business. I felt the right thing to do was tell the person that I'm close to what I saw. That person in return got mad at me. They still ended up staying together. So, it's a chance you take that might turn bad for you.
This is a good topic, I would not say anything. This could be a family member, a co worker or just a friend. It is easy to jump to conclusions and make a situation very uncomfortable. You don't know the mental state of your cousin perhaps, or the state of the their relationship. So much stuff is happening right now in the world, and it is best to stay out of people business because this could escalate really quickly. If that person is doing wrong, it will come out.
I would not say anything. You don't know what your cousin's current relationship situation is. Everything we see isn't always what we think it is. If the cousin's partner is doing something wrong, it'll be revealed.