@Cora, You must be really nice person and have been listening to others. Time to have a break? It can be difficult, but facing breast cancer is tough. We need to look after ourselves even though sometimes I feel selfish. This stage of our life is not normal. I think if they are friends, they will understand you later. time will help?
I looked after this lady she had a spinal injury and was unable to move independently and suffering from pain. During her hospital admission, her neighbour called her and stressed about the dog running away; when she hung up on the phone, we laughed. People don't understand what you have been through but some will. Maybe your neighbour, colleagues, an old friend of yours, someone will listen to you.
All the best.