I deeply hope you won't give in to this temptation but will cut off any relationship with this person at once. It may seem exciting and fulfilling at first -- but it's a dead-end road, and will only lead to heartache, guilt and sorrow.
Almost every day, in fact, I get at least one letter from someone who's allowed themselves to be trapped by this temptation -- only to discover that it failed to deliver the happiness they were seeking. Some even allowed a relationship like this to destroy their marriage -- only to be rejected by the person with whom they'd hoped to spend the rest of their life. The Bible warns, "There is a way that seems right to a man (or woman), but in the end it leads to death" (Proverbs 16:25).
Instead, I pray that you will recommit yourself to your marriage, and do everything you can to rebuild its foundations. Perhaps your husband has been a disappointment to you -- but have you allowed yourself to become a disappointment to him? Take the initiative, and little by little work to rebuild your relationship.
Most of all, make Christ the center of your marriage -- and your life. He can help you become the wife He wants you to be, and give you a new love for your husband. The Bible says that in marriage "God has joined the two together, so no one should separate them" (Mark 10:9, NCV).