Your boyfriend should not be reading your private mail. End of. Your ex is in prison because he was found guilty of a crime. He is responsible for his own behaviour, not you! You didn’t put him there, he did.
I hope you can get away from this new man. It really isn’t for him to tell you when or not you may be ready to take on information. Sometimes there is no good time and it’s certainly not up to him to decide on your behalf. Whatever next?