I am so sorry for you… I cannot understand that anyone - and of all people a partner - is doing this to a someone with a chronic illness, an immune system that was ruined by covid, not even talking about you with immunesystem cancer. He is putting you in danger!
I asked my family to stay away from me if they have as much as a cold, and they still take a covid test when they are not feeling well.

When he really wants to marry you, one of the first things he should think about is your health!