1) Get yourself something to focus on besides the marriage. When my ex first cheated and I was DBing him, I started training to climb Mt Whitney. Years later, when he left (after initially reconciling and having several good years) I bought a drumkit and learned to play the drums at 52. Shifting the focus away from what's going on for a while is very healing.
2) Realize you cannot control his actions. All you have power over is yourself. You do not have the power to save him from making bad decisions for himself. But I can guarantee you one thing - he is MUCH more likely to come back to you if you are living an interesting, exciting life than if you are balled up in a corner crying.
3) Protect yourself financially. A lawyer can give you good advice on what you can expect and how to make sure you are financially protected. Don't confuse the business part with the emotional part. Even if you divorce him to protect yourself financially, it's always possible to get remarried if he comes to his senses.
4) This is a unique opportunity to spread your wings. What have you always wanted to do that you haven't pursued, because he might have thought it trivial, or crazy, or he took up too much of your time to pursue it? If you were writing a book about a plucky heroine reinventing herself and finding happiness after a divorce, what would she be doing? Do that! Do you want a new haircut or color? Do it! Change your wardrobe. Pursue your bliss.
Believe me, there is life after a divorce even from a long term marriage.
