Did you confront him about the same? If it is an instance of singular cheating and he is willing to call it quits with her and make a fresh start with you, you can seek counseling to overcoming infidelity in your marriage. However, if it's a recurring habit and he is a serial cheater, leave him pronto and make a fresh start. Life is long, it's best to not continue bearing the burden of such a destructive relationship. Leave him, start afresh. Build your skill set, chart a new career course and get goals in life and strive towards revaming your life.