@lisa1471,
Stay out of it, Lisa!
It is their marriage and they will work it out. It is not your job to interfere,
no matter what you know or think you know. I almost can guarantee you
that you will lose your friend should you tell her about her husband's infidelities.
She will resent you for being the one who told her and who knows, they might work it out and she might forgive him, but she never will forgive you.
I repeat, other peoples marriage is none of your business - butt out!