Have you ever been in a relationship with someone and then turned crazy?

Their personality changes so much, it's like you don't even know the person anymore.
Like maybe they used to be mellow, not use curse words, never yelled, was very lovable to you, etc. Then they weren't the same. Everyday you noticed something different about them and they just kept getting worse?
What did you do about it?
Have you ever been in a relationship with someone and then turned crazy?
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