I doubt you are terrible, just human. Consider:

1. Coworker might put on pretenses like your husband. 2. Spouse has an unfair disadvantage. Coworker is new/exciting. You don't face big life challenges together. 3. You have little chance to fix your marriage while cheating. 4. Have you told your spouse what bothers you (even if it's monogamy)? 5. If you leave your husband for this guy you might have HUGE regret. You might miss him or your coworker might be disappointing.

However fixing a marriage can be slow/rough. It might never work & life is short. My married coworker has been unsatisfied for years. They are kind of codependent but they might be unfixable. She doesn't want to leave him, he doesn't want an open relationship. So she started an affair with me. This brings intense pros and cons.

Cons: 1. Immorally deceiving the husband. My AP thinks this will hurt him less than leaving but might be wrong. The guilt can be horrible. 2. AP can use this to hurt your career/finances/marriage/friendships. These risks apply if you get caught too. 100% trust is key including after an affair ends. Do you know your coworker well? I worked/talked with my AP for years before we started.

Pros: 1. It can decrease tension in the marriage. 2. Passion/infatuation can be heightened and prolonged by the nature of an affair. Great sex, love letters etc. If it's good, it's REALLY good. You can maintain the euphoria for years. (But this can make the end even more brutal than in a normal relationship.)

Last thing. Do not discuss this with any friends/family you can't 100% trust (which might be all of them). You're right, you can't untell it and it might hurt you later.

I can try to answer questions if you respond or PM me. These things can be more complicated/gray area than Reddit usually admits.