Am I being selfish?

You are absolutely deserving of respect. Your loyalty and preparedness to face this when you have so many reasons to leave should earn you respect in bucket loads. But I think you may need to accept that your H is not going to show it to you. He has never treated you well, and the impact of his illness are unlikely to improve him. They will just give him an excuse. It's typical for all sympathy to be directed to the person who is seriously with little to no thought for the carer who faces their own struggles, so his family's reaction is no surprise. Whether he wants people to know or not, you are entitled to share your experience with people who could support you. So I would certainly be confiding in a friend. You need that. And he doesn't need to know.
You could also try mentally and emotionally leaving him. So while you're there in body, you restrict your engagement to the necessary and superficial. You don't let him into your head and you focus your thoughts on the parts of your life that don't include him. It's almost like he's your job, or your house mate. It can be very helpful when you feel stuck.

My dear, you will not get any respect until you respect yourself. And you don’t.

He has done a number on you and if you stay you are proving to him and your children not only that it is ok for him to treat you this way but that you expect it. Your only option is to leave - if you want the best for you and your kids.

No one will thank you for staying with him. You won’t win any good mum awards or best wife accolades. Your spirit will die and you will get older and more invisible until there is nothing left.
You stay because you are afraid and it’s ok and it’s understandable. But sometimes the wolves outside the door are just imaginary but the wolf in your house is very real.

Tomorrow is a new day. You need to walk out that door and not come back.

I'm so sorry for what you are going through.

To be honest, I think you need some outside perspective, can you call Macmillan? Or get in contact with the cancer care team at the hospital if there is any support you can access?

Cancer puts a bomb under any relationship, but the one thing I would say is that the illness is not yours to carry.

Please really have a think about why you can't leave now, is it really only what the kids would think?

There might be real positives to having separate households, he can recuperate in peace during treatment rounds - treatment side effects can be distressing for children to witness and they can have some true respite.

A strong relationship can navigate cancer, but you may need to make a very very tough decision based on your situation - not the fantasy of a supportive team.

Obviously this all depends on Stage/type of cancer - but it can be a very long road with no obvious finish point, so if not now, be clear on your mind when.

He sounds like a horror.
Typical abusive pig wanting everything to be secret.
Stop listening to him.
He is not a good man.
Start telling the truth.
Just because he is ill does not mean you have to tolerate this.
He doesn't deserve it.

You're having it really rough OP. I'm sending you sympathy and strength. It must feel like life is battering you from all directions, and without the foundation of a supportive mutually respectful relationship to sustain you. I think the only way to get through this is to look outside for support for you to help you do what you feel you need to do for your H (you don't have to stay, but I get why you feel you do). Do you have good friends who you can spend time with to off load and give you a break from him? I think its really important to build and keep up a life outside of him to give you the strength to cope with him. Also reach out to cancer support groups. There will be other people in similar situations.

He doesn't want you looking after him so don't. Leave. That's the only and obvious answer. Leave and don't look back.

I’d carry on with my life op. Make sure there’s food like he did for you, see friends and do things that make you happy. In front of the children you smile; and if they or he say you should be doing x for dad you can say clearly and firmly where were you when dad wasn’t doing that for me while I was ill? Does he deserve care more than I did? I looked after myself, while here I clean the house for us both and cook so he gets more care than I did, and I get less thanks than he did. In life children you sometimes reap what you sow.

An arsehole with cancer is still an arsehole.
You don't have to do anything for him or stay with him just because he is ill.
If it was a sudden change of character along with his diagnosis I would suggest more sympathy but its not

But she said 6pm in the first place

Well I can understand why he wanted to finish his drink tbh!

She could have come to you

“Does that mean that they see you as a villain and that he can do no wrong?”

I’ve seen a very nasty, manipulative father twist the narrative in his children’s minds until they absurd see their mother as the villain. Think Grima Wormtongue

This, OP.

For now carry on being yourself with the children but grey rock him. He says he doesn't want you to look after him...don't.

If he starts being abusive, leave the room. Don't answer back just say 'ok'....most people need fuel to put on the fire and feed off your reaction. Don't give him one.

Start mentally sorting things out so that you are in a position to leave when the time is right.

The children would never forgive you?

Does that mean that they see you as a villain and that he can do no wrong?

Can I ask if it is ever going to be financially possible?

Also treatment only lasts so long? When is it due to finish?

Do you have your own bedroom or are you sharing with him?

Have you had any legal advice? Since you're married, you'll be entitled to a share of the house and potentially other assets.

You don't owe an abuser didley and he showed you no concern whatsoever when you needed support. You're deluded if you don't think your children have experienced his abusive behaviour and I find it difficult to believe that someone so self absorbed was a good dad.

How old are they, OP?

hugs for you, by the way xx 💐
emotional abuse is horrendously damaging 😞

He can fuck right off. I wouldn't lift a finger for him. I'd be telling him he's on his own, so he'd better find someone else to take care of him. Maybe he'll learn that his abusive behaviour has consequences.

He doesn’t want you looking after him.
Grant him his wish .

Your children will have seen and understood more than you think I suspect.