For goodness sake don't alienate them more. It seems a little selfish to have gone with a cold or the end of one in the circumstances and I am with them re-shopping centres, I don't imagine you have to go, we have a fortnightly shop and I have been to a quiet supermarket half a dozen times since early March, we are lucky in having lovely countryside and beaches to walk but I really don't need to go to a shopping centre, do you? If you like shopping and it is your 'hobby' I understand but there are other things you can do. I know that sounds harsh and I do have sympathy with your situation but you could have 'Christmas' outdoors in the summer or when we've all been vaccinated, that's what we're doing, imagine how bad you'd feel if you gave covid to them or how guilty they'd feel if they gave it to you. I'm sure they don't mean to upset you but decisions have to be made. Try to plan a nice time for the two of you, special treats in the food line, a good film, special presents (though my husband and I are giving eachother a week away when we can rather than presents), a good walk if the weather is nice or whatever you like doing and are allowed. If you can change your attitude of mind you'll have a much better time than if you are determined to be miserable, I know it's hard, I'd love to spend Christmas with family, but it won't happen this year apart from on zoom