How can someone be so thoughtful, nice, put you first, care for you then turn everything off?

How can someone be so sweet. Do everything with you, listen to you, put you first, push you to be a better person, been there for you, then when u jump into a relationship with them they want to l control you, they want you to not be you, or have a life, be with your friends do things you wanna do that makes you happy because it makes your selfish, and just shuts off his feelings, has no remorse of calling you names, isn't the same person he was?
How can someone be so thoughtful, nice, put you first, care for you then turn everything off?
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