My partner is struggling more than I am.
That is common and it does not mean they are weak or that you should manage it for them. They are watching something they cannot control and they usually have no role in the room.
Two things help more than talking about it. Give them a concrete job, medicines, questions, driving. And let them see a counsellor separately, so you are not the person they have to be brave in front of.
Written by two physicians. Checked against patient information from the US National Cancer Institute and Cancer Research UK.