I have read and re read your post and have struggled to see how you could have done things very much differently,the consequences would have been much the same.
Yes you could have done it sooner, just fessed up and bit the bullet. But you didn't.

I will be honest, I don't believe human relationships are meant to last a lifetime.
We are too mutable, too prone to be changed by our experiences, our age our work out friends. To expect two people in continual transition to last a lifetime in a relationship where the person they fall in love with will most likely be someone else in a generation's time, less if your younger and changing more rapidly.
It just isn't practical,ideal? Maybe, but likely, no.

Feeling guilt is an acceptable part of leaving someone, but only answer for what you yourself are directly responsible.
Your wife's ill health, sickly parents and bad drs, are not something you should hold onto as your fault.
Being unfaithful, and not quitting sooner are things you should take responsibility for.
Your not contesting assets, that is entirely up to you, but do remember you will have a life to fund. Don't leave yourself destitute out of your guilt.

As has been said before time is your friend here, but also not allowing yourself to wallow.
Try and do something once a week that gets you out, that reminds you how big the world is. That reminds you there were things you once enjoyed.
It's still early days, stick at the therapy.
I wish you all the best for the future. Take Care.