Jen I have a friend whose partner had the same cancer as mine I was asked to contact him which I did we talked but my offer of help was not of any benefit to him if someone withdraws it is very hard to find a way to help,I have become friends with his partner ,we meet for coffee occasionally she has a medical background and has helped me out on occasions with advice,she had similar problems with her partner withdrawing but she was not suffering depression like you .You are doing the right thing by going in to self preservation mode or you may have a huge setback with your own health,it is not selfish but the right thing to do,if your depression sends you,so low you are no good to yourself or him,so look after yourself first.
Kj