I am sorry to be so blunt, but the truth is what is needed.
Your boyfriend has a genuine disease. He is an addict and he is not in recovery. This means that he will use people, lie, and blame others rather than take responsibility for himself and his hurtful behavior.
Yes, reading his emails in the way you did was wrong, but he is using that as the excuse to make you feel guilty rather thane deal with his lying, cheating, and stealing.
Don’t waste more of your precious energy on him. He would need to be dedicated to a recovery process and immersed in that recovery for a good long while before he would be worthy of being trusted again.
Move on. Learn these lessons and be grateful you learned all this before you made the mistake of marrying someone devoted to using you and not taking responsibility for himself.
As you end this relationship I would strongly suggest individual therapy. The find help tab at the top will help you locate someone inn your area.