Good to get the whinge out.
I suffer from that feeling guilty crap too. It's such a stupid emotion! Useless in this situation.
It sounds like the two of you both need to cut yourselves some slack. Be gentle with yourself, be kind to yourself. Tell the old boy to be gentle and kind to himself. Tell each other your fears, name them, and then metaphorically throw them in the river and watch them float away.
Then have a little of what you fancy, toast the day, and tell each other your hopes, and make a plan to do something nice when all this is over, something to look forward to.
Maybe you can both check out this website:
https://www.otisfoundation.org.auI've been to one of their properties and it was wonderful.
If your chap is open to it, maybe he should read this:
https://www.bcna.org.au/understanding-breast-cancer/talking-to-family-and-friends/information-for-partners/You'll both feel better after seeing the oncologist and there's a plan in place. Big hug, K xox