Find out what she is missing in your marriage and try to give it to her. Be caring and understanding towards her and listen to her every day to find out what she needs. By giving her what she needs, you can reduce the risk of further infidelity.
Some couples play a game of make-believe, where each of them pretend to be someone else, during some or all of their lovemaking. In that way, they can get variation without the risk of actual physical infidelity.