My brother stole his sister and said it.

As a sister, you can consider the following suggestions to deal with your brother's cheating behavior:

1. Keep calm: It is very important to keep calm in the face of this problem. Don't let emotions control your behavior, and don't let emotions affect your communication with your brother.

2. Honest dialogue with your brother: Honest dialogue with your brother is the first step to solve the problem. You can express your worries and concerns to him and ask his opinion on this issue.

3. Respect your brother's privacy: Even if you think his behavior is wrong, respect his privacy. Don't try to reveal his secrets or expose his behavior, which may do more harm to your relationship.

4. Provide support and advice: If you think your brother needs help, you can provide some support and advice, such as seeking psychological counseling or marriage counseling with him.

5. Give time and space: When dealing with this problem, give your brother enough time and space to think and deal with his own problems. Don't be too strong or force him to make a decision.

Finally, you need to make it clear that your role is a supporter and consultant, not a decision maker or a substitute. No matter what you do, you should respect your brother's wishes and decisions and do your best to maintain family harmony and unity.