That's a lot of feelings Blue Sue. Short answer, I would not try to have major surgery and do heavy work on my marriage / consider ending it, all at the same time! That is way too many stressors for you, your kids, and your husband whom you do seem to respect. Hold tight a while and don't do something impulsive. A few more months won't matter. You can pursue the ideal life when you are not going through this scary heart stuff, I'd say . . .
I suffered from depression around the time of my heart stuff (before and after) and I am wondering if this could be the case with you. I know that during depression it seemed like I'd "always" been unhappy and that I'd been unhappy "for years" with my husband, even though objectively, like you, I could say "This is a good man." Today, I can't imagine why I would have wanted to break up with him. It was the depression talking and horribly distorted. So I am glad I went with my intellect instead of those distorted feelings and waited it out (and did all I could to get rid of depression including meds and lots of books and happiness exercises, healthy habits, etc). There are some books related to heart surgery and depression that others have recommended and I would recommend "You Can Feel Good Again" by Richard Carlson to help with those general feelings of discontentment - also "The How of Happiness." You can probably use some reading that will lift your spirits.
For the surgery itself - chances are really excellent you're going to be fine, your kids will be fine & you'll be in their lives a long while yet . . . try to talk back to those "cry-producing" thoughts.
Post-procedure (I was fortunate and had a balloon, not OHS - that's still in my future) I've definitely cultivated a joy-filled life, lost 50 pounds and appreciated life much more--but I didn't have to get a new husband, job or change anything major to do that. It was all in my perceptions and habits of thinking. And maybe some biochemistry too. I think there is something to that, with heart problems and depression. I actually had an article in Experience Life magazine about my journey out of depression, it's here:
http://experiencelife.com/article/a-happy-new-year-deb-sweeneys-success-story/
I hope something from all this is helpful to you - you have a lot on your heart and I hope you can lay some of it aside and deal with it one thing at a time - or that some will turn out to be not so heavy after all.