Maybe the situation with the cancer is pushing the feelings more to the surface, but they've always been there.
This is exactly right IMHO. The cancer is shouting at you loud and clear that you're vulnerable, that you need other people, that you love the people who are close to you so much that it hurts... AND you may also be identifying with your dad, too... he didn't fight (so it seemed to you) and now you're thinking you wouldn't fight if if if...
You are a soup a stew a minestrone a bouillabaise of feelings, my man.
What Martelo said, too: who cares what the reason is?
I just took myself to Sonic! I got out of the house in my wheelchair and left it beside the car in the driveway while I drove into towm. Yippee!
While on that excursion, I came up with another bit of advice: I see both you and Miss IC judging and evaluating yourselves all the time... if you can possibly manage to cease judging so much... and that includes positive judging as well as negative judging. Try to take a rest from grading yourself on how you're "handling things," how you're feeling, how you're doing.
Sometimes when I find myself judging myself all the time, I just say the words "no judgment" over and over again... especially when I'm trying to fall asleep.
The cancer has indeed brought a lot of dormant feelings to the surface. You will need to work through them, but you don't have to do it all at once.
Also, you have NO way of knowing HOW you would react if your W and kids were not in the picture? That's one of those "roads not traveled." There are SO many variables... if if if if if...