Andrew should be kept, possibly in a coma, or going from hospital to a convalescent home or rehabilitation centre. He could lapse further into the background. I thought the suggestion about memory loss was a good one. There are a number of posts which suggest his being written out could somehow "liberate" Anna's sexuality. WTF? Talk about superfluous. This is a woman who has sex with her boyfriend's father with the BF right there, next to them. Anna has sex with men, women, young, old, black, white, working class, middle class, in private, in public etc. etc. & with no extra liberation needed. If her sexual appetite expands any more she'll be a danger to herself & others, (plus also very tired).
Andrew provides a much needed anchor in her life & also a figure to cheat on, for those who enjoy that aspect. Keep him in.