I get the promise thing. I do. I get that your word is fundamental to who you are. I guess in every other area of your life, every day, every interaction you honour those values. Does breaking one commitment, when all your others are in tact, detract from who you are? Sometimes the exception proves the rule.
Interesting, since vows are a promise. Are you suggesting it's okay to break both his promises -- to not be unfaithful and to not threaten divorce -- or just the threatening one?
Since my husband thinks it's "just sex" and not that important, then, theoretically, it shouldn't be important to him if I have "just sex" with someone else. The rest of our marriage is fairly tolerable, and there are a lot of reasons to stay, just this one "little" issue. I'm a good wife in all the other categories. Yet I think forsaking that one promise of fidelity would, indeed, detract from who I am (or, perhaps, thought I was), redefining it to a large degree.