question

The picture you painted of him in your initial few post has nothing to do with his sister in law. They show he is insecure , in sensitive, does not trust you . These are not mistakes , this is his personality. This is not a war between his sister in law and you , it is about how you are going to lead your life if you get married to this guy.
If you feel that you over exaggerated about his personality and his behavior patterns then you are the best judge of him and yourself.