'Sets your self image on fire' – this reeks of childish justification, and the romanticisation of something deeply unethical and harmful.
As to personal experience – as a teenager in a very abusive relationship with a guy who was several years older and treated me horrendously, I did skirt the line of cheating with another guy, but immediately tried to break up with my abusive boyfriend. At no point did I think it would be acceptable to just carry on with both of them, and if anyone would've deserved disloyalty, it would've been him. But it doesn't matter how someone makes you feel, what matters is keeping your word and behaving with integrity – and at least having the decency to feel remorse if you don't.
You're also portraying your husband as a very pathetic person by saying that he was too spineless to leave his wife, but simultaneously he was willing to have sex with another woman for months, betraying his wife, letting her feel racked with suspicion and worry, and potentially exposing her to STIs via you. He might not have ever broken up with someone before, but that's not an excuse to cheat!
It does sound like a lot of your marriage framework revolves around trying to make sure that you both don't cheat again. Do you think it's normal to have to work so hard, and put so much thought, into actively preventing that?
And I see a post on Mumsnet practically every week where a woman who thought they were both too happy and exhausted by young children to cheat, discovers her happy, tired husband has been somehow finding the time and energy to cheat on her. The statistics aren't great for people who marry affair partners, from what I've read, but maybe you'll be the exception.