You are not selfish or doing anything wrong at all. I have a variety of suggestions that might be of use to you. Firstly, if and when you have a quiet time to yourself , can you think back to how your husband was before his illness. Would that man have wanted you to cope with everything you are handling now? Probably not. Then it might be worth taking a little time to have a notebook or a piece of paper and write down anything that you enjoy, whether you are able to do it at the moment or not.
So you might put gardening or did you used to go swimming, or walking with friends or visiting a specific place that meant a lot to you? Put a collection of places and things that you enjoy down, and then on a bad day you can look at them and choose something you would like to do or place to go to.
I would suggest that you start to look at a "day off" per week. So that you have something to look forward to for yourself, to give you something positive in your life to enjoy, which also helps you cope with the hard everyday life that neither of you asked for but unfortunately you find yourself in this place now. Dont feel the slightest bit guilty, but see the"day off" as your way of coping with the rest of the week. It should give you a little something to look forward too, and also to be able to look back on an hour or two you enjoyed the previous week.
Do get in touch with all and any people who can help you. Look at carers groups and for things like a day unit or group that he might go to one day a week at least. Speak to social services and your gp and explain that you are trying to organise a day off a week to ensure that you can carry on caring for him the rest of the time. You are more likely to be able to carry on with a weekly break and the various agencies will know and understand this. Speaking to other carers may also give you some good ideas for your locality.
Another possible tip is that I used to do 3 days a week hospital car taking people to and from hospital. Quite often family members would say how pleasant it was to be in the car as the person with dementia often sat more quietly and enjoyed the view as we went along and spent less time asking repetative questions. So if you drive you might look at simple things like a drive in the country and calling for coffee or tea somewhere. This would give the sense that you are still doing something together, but give you a little bit of peace and quiet.
Do you swim at all? Again a physical thing, which can release tension and give you some exercise. If he enjoys swimming and has done it in the past it might be a very good thing to do, as once you are in the pool, he knows what he is doing, you are visible but can be doing your own thing and relaxing a bit and the chance for some general conversation with other swimmers.
The important thing is for you to accept and recognise that you are not at all being selfish or self centred by doing these things. They are actually ways that you are managing to keep going in a difficult situation. When you are at home and he is rude and rather cruel, you might find it easiest to simply not reply but leave the room. Also I think it is a great idea to thump pillows and cushions and let the tension go that way.
Do stay in touch with GN's as you will find many people understand your situation and we try to be supportive of each other. There may be nothing we can do to make the physical situation any better but we are here to listen and support and help you recognise that you are doing the best you can and you do have a life of your own to consider too.
Whilst of course you want to share what you can together,you may in the future have to see that sadly you are not in that together situation that you were in. This is hard to cope with, but at the same time once it becomes that different situation, where you are a carer rather than a wife, you can come to see that you need to look to friends and hobbies to give you some personal pleasure and support . It will always be sad but can actually become less painful if you are not looking for any reaction from them , and can see that if he is being unkind or cruel, that it is not the person you loved who is doing this and so you can gradually let yourself be less concerned with what they say or do in relation to yourself.