I'm going to subtly flirt with my husband's brother
Why would you flirt with your husband's brother?
I like his sense of humor and he is also cute. He has similar hobbies as my husband and I like that too
It sounds like a terrible idea to flirt with your husband's brother. Thats the kind of betrayal most people can't forgive.
It's fine for my husband's brother to break my relationship or whatever.
Flirting with your husband's brother is completely wrong. It sounds like you are just unhappy in your marriage. If you want out of it then just be honest because going through this method to end your relationship will create bad blood and resentment most people won't ever be able to let go of.