Is your partner non-binary/asexual? If they just have no sex drive, never really did and went along with it to please you, I can see they might feel it's time for what they want, now.
Has something changed - menopause, impotence, depression?
Or is it remotely possible they're getting it elsewhere and are using this as a smokescreen?
Feeling upset over never having sex with your partner again is totally understandable.
Pressurising someone to have sex when they don't want to is wrong.
You can't change their sexuality.
You can decide if you want to stay with them - and accept no more sex.
Or you can stay with them, keep the relationship and find sex elsewhere.
Then there's the risk of STDs, deciding do you tell them and make an arrangement, or keep it secret - with all that that involves?