Catholics, what is worse: cheating on your spouse or divorcing your spouse?

both are mortal sins. Both can be forgiven in the confessional, but in the case of cheating, you can redeem yourself easier because you can try to work things out with your spouse. If you have already gotten divorced, it is a lot more difficult to get back with your spouse. Therefore you must not remarry or have any kind of relationships, because your marriage to your spouse is still recognized by God as a valid marriage, even if you got divorced, you are still married to that person in God's eyes.