I'm in love with my brother in law
What made you realize that you were in love with him?
I do not think he is a good husband for my sister really.
I hear what you're saying, but it is considered forbidden and an act jealousy if you cover your sister's husband. You should try and find a guy in a different environment, like your job or friend circle. Otherwise you might ruin your sister's marriage.
You don't understand, I love him and his cock is amazing.
Whether you think his dick is good or not, you are better off finding someone outside of your social circle. It is a bad idea to try and be with the partner of your sibling. All this is going to do is making your sibling resent you.