Hi Heather, I'd like to help you with your question.
It is very hard when you are faced with behavior that you did not expect. Your husband appeared to be loving and kind before you married him then suddenly changed. It would seem based on his behavior, that he was hiding his true nature from you.
From your description of your marriage, it sounds like you are in an abusive relationship. Abuse can include emotional, physical and/or sexual abuse. The main symptom of an abusive relationship is control. If the other person is trying to control you, then you are being abused. The other signs of an abusive relationship include:
feeling fearful of your husband
threatening to hurt you or kill you
blaming you for his behavior
taking away your freedom
refusing to let you have an opinion
no respect for your feelings
you feel as if you are walking on eggshells around your husband
jealousy and possessiveness
The most disturbing of your husband's behaviors is his threat to kill you. This is how domestic abuse starts. The attempts to control you and the threats if you do not comply.
Your husband knows enough about what he is doing to hide it from others. He hid it from you initially and now he hides it from therapists and others in your life. That means he has insight into his behavior and has no intention of changing. And unless he wants to change, there is nothing you can do to force him.
It is important that you get out of this relationship now. I know that is hard to hear, but situations like your marriage do not end well. Your husband is trying to control you now and most likely, his behavior will escalate given time. He will become more and more suspicious of you, even if he cannot find proof of affairs. This will cause him to try to keep tighter and tighter control over you and you may end up giving up everything, including family, jobs and school just to try to keep him calm. And many times, men who make threats to kill their spouses attempt it at one point.
You can get help through your local shelter if you feel you cannot leave on your own. Here are some resources to help you:
Please consider getting help now. An abuse counselor can help walk you through resources available to you and they can provide the support you need to leave this marriage before you cannot get out on your own.
I hope this has helped you,