Sometimes, some people misunderstand some actions and behavior but it’s your responsibility to clear their doubts. You should try to conduct an effective communication with your brother. You should try to make your brother understand that your sister-in-law is like a mother figure to you and you don’t have any ill intentions about her. It’s important for you to clarify all his doubts as you all are a family and these misunderstandings will only create a crack in your relationship. Therefore, you need to talk to your brother and resolve this matter as soon as possible.