Hi cutteduppear, - I'm sorry you are having problems.
I thought maybe it would be helpful just to give a viewpoint from the 'cancer' side of the journey, as I have also had cancer (DX 4 yrs ago like your DP).
I'd say firstly you don't ever move on from a cancer DX, - it is always with you. always in the back of your mind as a scary thing that might come back one day. My outlook on life definitely changed, - I tend to get on with doing things I want to do, rather than waiting and mulling things over, - I always feel a bit as if I'm on borrowed time.
Cancer can be quite an isolating illness, and it's hard to describe how it feels to people who haven't had it, so I think there is a tendency for people who have had the illness to share info. and views and talk about it quite a lot, because to some extent you can't really talk about it with people who don't know what its like, and also I don't talk about it much with my family because I don't want to worry or frighten them.
I think people have to move on in their own way in their own time, - I have passed the stage where I want to talk about it all the time, to wanting to forget it and get on with life, but this might not have happened for your DP yet, especially since his original prognosis wasn't too hopeful.
So all in all, it's a big thing for everyone involved, for him - he will have all sorts of fears and worries going through his head, - I've talked to lots of people who've had cancer and like me they all say this - we all get those four o'clock in the morning terrors every now and again!
Also - you have been through a 'cancer journey' too, and will have gone through many fears and worries yourself, - and I think often partners feel guilty for feeling low, or worried or unhappy, because they feel they have no right to feel bad because they didn't have the cancer. - Absolutely not the case, your feelings are as valid as they ever were, but I know it's hard for partners and carers.
Has your partner tried anything like counselling, or had any help from a cancer support centre? (Macmillan also have helplines for talking things through and IME are very good) sometimes professionals can help you get through the 'being a cancer patient' mentality, and beyond into a new normal, and they can do it objectively with a wealth of experience.
MacMillan might be able to help you too - you could talk things through on one of their helplines - they help families as much as cancer patients, - and they also have lots of relevant booklets about relationships and cancer, being a carer and how to talk to people who have had cancer etc etc. You can get booklets from their website for free, and most libraries will have them all.
It is very hard for you, and you sound so sad, but don't feel you have failed in your support, I'm sure that is not the case.
For everyone involved in a cancer diagnosis - patient, carers, partners - lots of feelings build up, anger, resentment, fear, sadness, - with each other and with the illness itself.
I hope you can get through this patch, and get your relationship back on track,
and I think you need him to make a commitment to spending time together and tell him that's what you need. Cancer is a devastating illness, but it's not an excuse to treat others badly and be inconsiderate, you've got every right to have your needs considered too.
Good luck 