I feel the same, the last few days it has really got to me. DH and I both retired a couple of years ago and were really enjoying ourselves, having moved to a new city. We had also planned several lovely holidays for this year.
Then, just before lockdown, he was diagnosed with an incurable and advanced cancer. At least we were fortunate in that he had brilliant and fast service from the NHS, who carried out a battery of tests in a very short period of time. He went from consulting his GP to starting chemotherapy in just over six weeks. The NHS target for carrying out the endoscopy alone is normally six weeks (which they often don't meet) and, of course, if he had presented a few weeks later he would not have been diagnosed at all.
The thing is that DH is being so brave and determined - he walks about seven miles a day, sometimes more, a combination of a very early walk outdoors and circuits of the garden. He is walking round now and it breaks my heart to see him. He then goes on his rowing machine for about 25 minutes. He is keeping himself as fit as possible and having a determined mental attitude, as those are the only things he can do - apart from taking the treatment and eating as well as possible.The chemo is not shrinking the tumours but they are not getting any bigger.
This was not how I imagined spending our time together, especially if it is limited. The whole scenario is like some awful nightmare. I even do social distancing and wear my mask in my dreams
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But - we are together and DD is with us, along with our dogs and her cat - we have a garden and the roses are coming out. We have books and music and plenty to eat and drink. I usually wake up weepy and feel better as the day wears on.