How could a girl that used to be my friend and then blocked me be a completely different person?

This girl that I was good friends with from counseling group, was a good person who cared about her friends, was married to the guy she called the "LOML", father is a pastor, a brilliant writer and artist, pretended to be a caring and kind person.

I found out from other people that she is cheating on her husband with multiple guys that he worked with, she went to bars and went to hotels to have sex with random guys, she hid all this from view, but friends tell me that she told her hi she was out with them when she was having sex with other guys.

She pretended to be someone completely different, how can someone do this to their husband, their friends and their family, lie and have sex with random trash, have sex with her husband's friends and coworkers?

Help me understand, because I can't I've been sick ever since I found out.

Updates
10 mo
She also blocked other friends after using them for money.
Updates
10 mo
Should I tell her husband? He deserves to know, but I don't really know him too well he's a decent hard working guy who doesn't deserve to be cheated on. Also HOW do I let him know without doing it directly?
Updates
10 mo
Thank you to everyone that answered, but it's not any better. I can't make sense of any of it. How can this person who I got to know so well, talked about things for hours at a time, I cared about so much, and now I find out she's this completely different person who lies to her friends and family and cheats on her husband with random guys... I don't want to love or care about anyone anymore because if someone you love and trust can lie and hurt others so easily without blinking, I just can't
How could a girl that used to be my friend and then blocked me be a completely different person?
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