TWR Now I understand the situation better, and I can say I was in a very similar situation.
A couple near me split up ,I and my wife were close friends with both of them. They were both in their 70s when they split and we had known them as a couple for 30 years. He left because his wife was unable to have sex any longer and he found another lady who promised him sex !
I was very annoyed with him. But it turned out his wife has had a far better time since he left. He was very controlling and did not let his wife have any freedom. Now she has a wide circle of friends (including us) gets invited out and on holidays , has friends to stay and generally is having the best time of her life. She is off on a 2 week holiday to Italy next week having only got back from 2 weeks in Spain in November.
So what I thought was a disaster has turned out to be for the best.
Something similar may happen in your friend's case. Yes I know the cancer makes it extra difficult but there could still be a positive outcome.
I also find it odd that you say you have a different attitude in real life from your AB 'persona' . I and I assume most others have the same view on here as in' real life'.