I think you have done a great job with all you're going through, and you've caught on quickly to the 'rules'. I'm proud of you.
Your family has had more than its share of struggles and heartache, compound that with hitting the mid 40s, and escape to a newer life can sound pretty good. I bet the thought may have crossed your own mind but your sense of love for your family and responsibility stopped you from beating him to it. And maybe fear of what you would lose.
Now the loss has happened, we know what the bad news is, and I'm not minimizing it. But the good news is, amongst all of the responsibility you have -- you get to reinvent yourself a bit. To bring back that spark, that feeling of 'you' inside.
What does your best you look like? What would you just love to be doing, saying?
Spouses very often do come back for better or worse. Do everything you can to enjoy being you. He might not see every detail but he will get the sense of the changes you're making. Do them (the things you love) for yourself so you will enjoy your life. And when you do, there is nothing more attractive. You will radiate confidence and glow.
Another benefit of that is your daughter will see how to handle heartaches and setback and she is at such a critical age.
I know you can do it from what you've posted. You 'get it'. You deserve the best.
sg Love is PATIENT, love is KIND, LOVE never fails / DB since 2001