I'm going to open my husband's mail
Why do you need to open his mail?
I don't like the way he's double-crossed me before.
Being double crossed is disheartening. Do not open his mail, that is against the law and rude. He can have you reported or even worse.
I would punch him in the face but he's at work. I just want to know what he's up to.
Punching him is absolutely unnecessary and you can be charged with physical assault that may put you in jail. I hope you just talk calmly with him and discuss the instant when you felt you were double-crossed. I do hope you work it out with your husband, I really do.