I need advise

My husband’s friend is cheating on his wife at work. I don’t personally know her, but I’ve known the guy for a long time, and it really hurts me to know he’s doing this to her. They have three kids, and he’s constantly having affairs with different people.

I’m torn about whether I should tell her anonymously about what her husband is doing. On one hand, I feel like she deserves to know, but on the other, my husband might be upset with me if I get involved.

What should I do?