First of all, my heart goes out to you. Discovering your husband’s infidelity must be a heartbreaking blow. It is important for you to seek safety and support to face the difficult decisions ahead.
In Catholic teaching, the bond of marriage is indissoluble. A truly valid sacramental marriage ends only in death. But couples sometimes discern that they can no longer remain together. Sometimes they obtain a civil divorce while remaining married in the eyes of the Church. Sometimes they can obtain an annulment, a declaration that in the eyes of the Church the marriage was never a valid sacramental bond. The latter is required if either party wishes to marry again in the Church.
The Church does not oblige you to stay with your husband, especially if you have endured some form of abuse or neglect. Neither would the Church insist that you leave. Ultimately only you and your husband can decide whether it is right to remain married or to end the marriage. If you decide to remain married, there must be a mutual commitment by both of you, assisted by a trained counselor, to work to restore the trust and respect that has been broken. If you decide to end the marriage, also assisted by a trained counselor, you must find healing and strength to begin a new moment in your life. You may also decide to pursue an annulment, as described above. My prayers will be with you.