I think my sister in law is so beautiful
What do you like about her?
I just love how much her husband loves her.  I love seeing them together.  It's so beautiful
It sounds lovely that you are so touched by the relationship between your brother and his wife.  However, even if you find her extremely attractive, you should not try to come between them by pursuing a relationship with her yourself.
I want to be happy too... no wonder her husband loves her. She is so perfect I need her too.
It is wrong to come between someone else's relationship. Do you think maybe you have created a false sense of reality about their relationship because you like her so much?