How can one just change 180? What happened?

This is the kind of thing I worry about all the time within my own marriage, even though my husband and I say "never" all the time.

We have a friend who told us recently that their husband asked for a divorce and it was a huge shock at first but after my husband and I talked about it, we now just noticed the past signs. I won't get into the exact details but our friend's husband became super political during 2020, I mean hard-core to the point where I didn't dare talk to him about it. Now he's anti of what he once believed in but still strongly political and became religious.

I am not saying that there is anything wrong with being religious. I'm aware that everyone has their beliefs so please don't think I'm against it.

Turns out his beliefs turned 180 and he slowly but now changed his lifestyle dramatically to the point where our friend has no idea who her husband is anymore. They are now separated and will be starting their divorce process.

It just makes me so sad because they had a beautiful wedding, which was 2 months before everything happened in 2020. They really were truly in love and made for each other, at least we thought they were. From a personal perspective, her husband was a fun person who was enjoyable to be around until we noticed the dramatic change 6 months ago. My husband couldn't stand to be around him when they both went to a mutual friend's bachelor party this summer.