I think Llimitless wrote excellently, and, as usual, DGU hits the nail on the head in just a couple of sentences.
LisaLives, I certainy agree that "pretzeling" yourself -- doing whatever it takes to please MIL, for example, isn't the way to go. you are right there. you are right about a lot -- the bit about sorting out your career, taking care of your kids, all that. That's living YOUR life.
We're all uncertain; I've had some experiences that I might call "knowings", but I know that my own fears and anxieties get in the way of those, and that I still have no idea if my H will turn back to me or not.
What I do know is that this takes a long, long time. I remember reading in the Divorce Remedy chapter on MLC (and it just glosses over it, to tell you the truth) that you should think of something that required more patience (I think that was the word) than anything you could ever imagine, and then multiply by a million and you might begin to have an idea. In other words just a huge amount of time.
It IS a process. For us as LBS as well, I think. I've gone through the thinking that I drove him away with my anxieties or what have you; we didn't have a cancer experience but do have children with special needs that pretty much consumed me for 10 years. And, like you describe, I used to never feel that my H was "in it" with me; he found it hard to deal with and found reasons not to participate.
Like you, I spent a lot of the first couple of years thinking "but I had no choice" but to deal with children situation; I, too, felt and still know that if I hadn't put all that effort in my children wouldn't be where they are today. At BD my H accused me of feeling that life had dealt me a "bad hand", that he just wanted to be light; I just got angry and thought that I'd be happy to be more lighthearted if I had more support with the serious stuff.
That was all before I really understood that this is a process. And I can tell you that it took me over 2 years to see that I hadn't accepted the process. And I'm STILL working on surrendering to it.
I know those feelings. I can tell you that in the intervening years H has admitted that the effort I put in was necessary (and he has also forgotten he said that...); I have watched him go through all sorts of things; grasping for the golden ring only to find that it wasn't the holy grail. But he continues to go his separate way.
It's so hard to separate out their actions from our feelings, if that makes sense; or rather, it's so hard not to attribute huge meaning to every action. My H continues to assert his extreme separateness from me/us; I still get a sinking feeling with each thing; must remember that it's part of the process rather than something very personal against us. And believe me, I know how hard that is.
Trust the process. And learning to do that takes time as well.