Regardless of having appearance of having good intentions one moment and then being an abusive jerk the next it is not OK to act that way. He is not coping and for whatever reason is taking his frustratuons out on you but his not coping cannot be made into your problem.
He may be acting like an abusive a-hole because he is not coping or could be because he is an abusive man and is using your physicall weakness to pounce and then uses 'not coping' to get sympathy from you for his bad behaviour. Abuse is not just physical violence - emotional and psychological abuse is just as bad if not worse... And you need support NOT abuse if you are to get better. What he is doing is making you suffer both emotionally and physically and that cannot be acceptable.
All you can do is tell him to get professional help to help him understand what is going on and to find a way to cope.
I do not know him or your history so really do not want to try and judge him and what his reasons are for behaving the way he is behaving but it is not a healthy situation for yourself and not healthy for your kids.
You have to find a way to get some peace so you can get the best outcome from your therapies. BC and beating it must be priority for you so really if there is any way you can get 3rd party help please try to do so. Since he is manipulating you having a 3rd party that is experienced in dealing with this may be the only way...
And when the active part of your therapy is done then you need to think of yourself and your kids long term. Sadly it is not just the spouse that suffers when someone is behaving the way he has been behaving. Kids are far more perceptive than given credit for and one thing you will need to remeber when this BC mess is over and you are re-evaluating that relationship is that exposing the kids to it is at the same teaching them what is 'normal' in a relationship and you will have to decide if you want them growing up learning that being treated that way is 'normal' and OK as dynamic between our parents kind of pre-programs us for life and we tend to gravitate towards spouses that exhibit that same behavious that we grew up with - even if bad and abusive ??
But right now, regardless of what he says and what he tries to persuade you into doing or not doong you must remember that you have to be No 1 so you can get better. Unless you get better there is no 'tomorrow' for resolvong problems... The fact is cancer is a deadly disease and you are fighting for your life here so he has to pull back as this is not just a a partner having a tanty and playing 'mine is bigger than yours' but a serious danger to your wellbeing so make sure you take care of you. If you can live together while javing treatent withiut allowing it to affect you negativelly hang in there but if this is getting to a point where your health is suffering you need to act to protect yourself and if you are not well at the end of this who will take care of you or your kids...
Do what feels right for you and ignore the rest...
All the best
Jel