Once you decide that you can't remain in your marriage, you will have to break the news to your spouse. This isn't going to be an easy conversation, but you can take steps to tone down the impact that it has on the nature of the divorce. You shouldn't ever bring up the divorce up in the heat of an argument. This is a conversation that is best handled when both parties are calm, and it should be done in private.
Make sure that you have your thoughts in order. Think about what you are going to say and how you will say it. There is a good chance that your future ex will have a strong reaction to this news. You need to decide ahead of time how you will handle this. Trying to remain calm during this can be beneficial since it might help to set the tone of the divorce.
When you are speaking about the divorce, try to speak of yourself instead of just pointing out what your spouse has done. This means focusing on "I" statements and leaving the "you" statements out of the conversation.
This conversation isn't the place to start talking about who is going to get what. Instead, save that for later once you've both had time to think about the split and what it really means. You don't want to agree to anything now that you might regret later.
You might need to get help to deal with the end of the marriage. Remember that addressing your emotions now can help you make sound decisions as the process moves forward.