Am I a bad friend if I tell the truth?

I have a friend who cheated on her husband and lied for years. They finally moved out of state but because she was so in love with the boyfriend, she moved back. She convinced her husband that she needed a break and makes it seem like they’re working on a long distance relationship. Her husband literally has no idea that she lives with another man. She trained her kids to lie for her and has her husband thinking she lives with me, which she doesn’t. She lives with the boyfriend.
Her husband came to town a few times to drop things off to her and he always questions why she’s never at my house, no matter what time it is.
she is so miserable with the boyfriend because he treats her so badly- which is probably her Karma. But because she is so deeply in love with him she doesn’t care.
I have started to distance myself from her because I can’t take her lies and the stress from her always venting about the pain the boyfriend causes her.
I’m stuck between a rock and a hard place because whenever the husband comes to town, he will drop things off for them and he’ll ask me questions but I will literally keep it short and go back in the house. Even though I hate that my “friend” is making certain decisions that I don’t agree with, I don’t feel like it’s my place to tell on her.
I just feel like if I tell on her, I’m not a real friend.

Do I betray her and tell the husband or do I mind my business?

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Just to give more explanation because a lot of responses are assuming that the husband is in the dark and knows nothing.
However, the husband been found out about her cheating. After she started to cheat is when they actually got married, specifically because he thought it will stop her. She was too far gone. When the boyfriend started to come to her house and make things worse. That’s when they moved out of state. Sadly she got pregnant and moved back to live with the boyfriend.
Am I a bad friend if I tell the truth?
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