Extramarital affair

My heart broke when my husband revealed about his affair with his colleague who is unmarried. He claims he slept with her only once which was about 2 yrs ago but feels guilty of doing that. Now she is emotionally connected to him and wants him to be with her forever. My husband wants to get rid of her and wants her to lead a happy life by getting married. He feels bad of cheating me and spoiling her life. Pls suggest