@JustaGirlTrying I think that you sound absolutely lovely, and like a very caring person, and I think that your Dex is very lucky to still have you in his life.
I also think that to be considering offering him some respite care in your own home is wonderful of you. Having been a community health care assistant myself, and then a full-time carer for my own DMum who we - my husband and I - brought into our home when she was bedridden and needed 24 hour care, I am hoping that if you haven't already had any experience in caring for an adult, that you rectify that asap, by doing as much research as possible. Whether you are just intending to give him nutritious, and possibly light meals, keep him hydrated, keep his clothes washed, and possibly to give him the correct medicines at the right time (a district nurse, or a dr, should explain that to you if you were willing to take on that responsibility), and basically just keeping him company, or are you actually considering a much more intimate roll with you maybe having to deal with single or double incontinence? if that is on the cards, and if you have not had any experience in dealing with adult incontinence, then you would definitely need some training or experience in dealing with that potentially difficult job.
If your dear friend and ex, is that seriously ill, then you could probably arrange with SS to have professional carers come to wash, change and dress him up to 3 to 4 times a day, but honestly when that was my paid job, going around individual homes out in the countryside, to give intensive care, it eventually became soul destroying as apart from the awful working conditions, I couldn't help but get personally attached to some of my clients, and attending their funerals afterwards was quite often harrowing, and they had started out as strangers.
So please don't offer him recuperative care, or on-going "towards end of life care", in your home OP, until after you know his prognosis, and what, if any, hands on care he might need. I really do think it is wonderful of you to want to be there for him, but to do so in more of a visiting supportive friend type of roll, might be better for both of you, and more realistic. I have just remembered that I think you said you have a bad back yourself OP - but I could easily be completely wrong about that - but if you do have a bad back then please, please, please, don't take on any heavy lifting, or awkward handling roles, as you could end up like me, in a wheelchair with severe arthritis in my lower spine. When I transfer, or try to take a few steps, my back feels like it has a sharp knife being constantly punched in and out of it.
I first started my so called 'caring career' when I was in my early twenties, and when I had 2 very young children at home. I only did longish weekend work back then, when my - then - Dhusband could fully take over the children's care whilst I was at work. There weren't any manual handling rules at that time, or if there were, the nursing home I worked in certainly didn't give me any training in ilthem! By the time I took up the CCW in the late 1990's (approximately 15 years later, and in another part of the country) we certainly had manual handling training for the first 2 days of my employment.
But unfortunately, when you are out in the community at about 10.30 in the evening (often in a very remote house), and your client starts losing their balance while you are trying to give them a wash down in their tiny bathroom, you just instinctively catch them any which way you can! The cluents often wanted to - quite understandably I think - stand in their bathroom, rather than have me take a warm bowl of water, soap, flannels and towels, and moisturising cream for their arms, hands, legs and feet into their lounge or bedroom, where I could have done most of their wash while they were sitting down, as I think it made them feel more normal to be standing in their bathroom for a wash down, as that is what they would have often done before they become too disabled, or too old and fragile, to do it themselves - most of them would have been born in the early parts of the 20th Century.
So anyway, you lovely lady, please do lots of research before offering your DFriend a respite holiday. Another consideration - at least partly depending on what type of cancer he has, what stage it is at, and how aggressive it is - is that it might become emotionally difficult for either him, or you, or more likely, for both of you - to send him back to his/his parents home, or even back into hospital, or even worse (because of what it would mean, rather than the amazing care he would receive there) into a hospice.
If he doesn't want to leave yours, but he can't continue to stay with you (for whatever reason, as any of your reasons would almost certainly be valid reasons), then that could become incredibly difficult for you.. Older people going into care or nursing homes, or any other establishment that means they will almost certainly not be able to go back to their home, or wherever, forever, will quite often beg their loved ones not to send them away, sometimes even saying that they will never be awkward, demanding, or make a fuss again, which is - imo - one of the worst things, and therefore, one of worst feelings in the world to have.
Without knowing what type of Cancer he has, or what stage it is at, or how aggressive it might be, it is hard to try and give you anymore advice. However, if after hearing all of that, you still find yourself wanting to invite him into your home, knowing that the possibility of you needing to take on an intimate care roll for him if necessary, or allowing strangers (care workers) to intrude into your own safe place (unfortunately, it often does feel like an intrusion) for goodness knows how long, then may I suggest that if you have something like a Leonard Cheshire Nursing Home, or any other type of nursing home near to you, it might be a good idea to see if you could become a volunteer carer for at least a few days, or preferably, weeks.