Awfullyconfused, you never mentioned how you managed to meet back up with the former boyfriend, but it sounds as if you're banking on a fantasy: you've somehow developed this idea that your life with the former boyfriend would have been some glorious experience rather than dealing with grinds of repetetive daily living. There is also not enough information about your legal husband - NPD? Abusive? Or, are you just bored with your relationship.
Replacing one problem with another accomplishes one thing: different problem, same issues. Perhaps, you might want to focus on filling that void in your Self (that Life's Spark that makes you unique in all the world) with your Self - find something that you've always wanted to do and nurture that interest.
Your current situation sounds like an emotional train wreck - just as a previous response suggested: you are setting your Self up for disaster, without a doubt. Playing the "Woulda-Shoulda-Coulda" game is fueling something within your Self that is lacking. Of course, if your current spouse is an abusive NPD, I'd remark about that, as well. But, there's really not enough information and, what you've provided, is suggesting boredom, self-esteem issues, regret issues, etc. Having an affair with someone (old flame, or otherwise) will not (ever) solve the core issues.