You never imagined yourself being faced with that question but here you are, worried about your current marriage situation and the possible outcome. There's nothing to do but admit it and seek for a solution for you and your partner's conflict.
1st Rule of How to Save a Marriage is to Admit your Guilt
Admit your faults and shortcomings. It's really difficult to do that for someone especially if faithfulness comes in issue. Perhaps, nothing hurts your spouse more than for you to cheat on her or him, but that needn't be a reason for your marriage to end.

