If you want something to say to her in parting, keep it simple and honest.
Letting her know that you love her is fine, just don't go over the top with it.
You should definitely let her know that you take responsibility for your actions and that you are devastated at the affect it has had on her and your family.
And you can let her know that all she ever has to do is call if she needs anything.
And note that the writing above is FAR more than the words you need to be saying in quantity. Again, keep it simple and honest.
Be a present Dad. Take every opportunity to see your kids. Make an effort to normalize that schedule so that their lives are not in any more turmoil than necessary.
It's a lot about attitude for you right now. As Sg said, you have to OWN the impact of your medical problems on the family. You have spent so long trying to convince your wife that it was medical and out of your control. To her that sounds like you are excusing yourself. She NEEDS to know that you understand how rough it was for them, and that you are terribly sorry for all the problems you had.
They say the journey of a thousand miles begins with a single step. Well that's about what you're facing here, a thousand mile journey. And these are just the first steps. The road is long and often difficult, but if you are a man of honor and integrity AND you are committed to bringing healing to your family, you will continue step by step to travel this path.
Know going in that there is not much in the way of rewards along the way. Your eye is on the final prize - a family restored.
Blessings,
Bill
"Don't tell me the sky is the limit when there are footprints on the moon."