My(25f) best friend(24f) has been cheating on my brother(25)

EDIT : I made a typo. My brother is 26; one year older than me.

The two of them are married. She and I went drinking together. When she was really drunk, she confessed to me that she pressured him into quitting his job and becoming her stay at home husband so that he would be financially dependent on her and unable to leave her even if he finds out she has been sleeping with other men.

The next morning, she confirmed what she told me when drunk is truthful. Now I know that I should tell my brother he has been cheated on. But I just couldn't find the right words for this. What do I do?