If I were to date my sister's boyfriend's brother, would that make us related somehow ?

No. They aren't married. Even then it would be distant. You aren't related to a friend of a relative.

But if my sister and her boyfriend were to marry would that make his brother related to me if we went out ?

but if my sister and her boyfriend were to marry would that make his brother related to me if we went out ?
No.

His brother would be your brother-in-law (your sister's husband).

So if my sister and her boyfriend were to marry does that make his brother related to me if we went out ?

sister = sister
sister's husband = your brother-in-law
sister's husband's brother = no relation to you

WG, I am apparently on planet zippy.

Yes, the sister's husband is her brother-in-law. His brother is her... nothing.

so if my sister and her boyfriend were to marry does that make his brother related to me if we went out ?

You can re-word this and ask it in many different ways but the answer is always going to be the same.

How about if the sister and her boyfriend marry but she doesn't go out with the brother.

Are they related then?

so if my sister and her boyfriend were to marry does that make his brother related to me if we went out ?

It doesn't matter in the least whether you go out with him, have sex with him, or share a plate of nachos. The only way you can become related to someone with whom you don't share ancestors is by marriage.

If your sister is married, her husband would be your brother-in-law.

His brother would be your brother-in-law-in-law, I guess.

http://en.wikipedia.org/wiki/Affinity_(law)

The sisters brother would be related to you by marriage, not blood. He'd be your brother in law if they marry.

The brother of the sisters boyfriend would be the brother of the sisters boyfriend, and that's it.

Heck, if you wanted, you could have a relationship with the boyfriend of your sister, even if they're married. Wouldn't make you a good person, but not because you're sleeping with a relative, only because you'd be sleeping with a married man, a man married to your sister no less.

I don't understand why this question is in the legal forum. What does dating have to do with the law if the person you're dating isn't a blood relative?

How old are you?

You can go out with him because even if your sister married her boyfriend you still would not be blood related.

You can go out with him because even if your sister married her bf you still would not be blood related.

Thanks. I was having trouble wrapping my mind around the absurd suggestion that dating, or BF/GF could somehow constitute an affiliation or family relationship. :)

Thanks. I was having trouble wrapping my mind around the absurd suggestion that dating, or BF/GF could somehow constitute an affiliation or family relationship. :)
My husband's father and his brother just happened to date and marry sisters. It all worked out. All the cousins from those two unions looked a lot alike. :)

Yeah I even have heard a lot of stories of twin guys marrying twin sisters in a double ceremony.