The point is really not how often any of us do it, but whether a couple are in agreement about what they do, how often they do it and so on.
Obviously, ill health can put the tin lid on sex within a marriage or long-term partnership. Spouses don't always feel the need of the same amount, but it should be possible to reach a compromise.
If both husband and wife really mean that they no longer want or need or enjoy sex, then I see no reason why they shouldn't still be able to have a happy marriage. After all sex is (usually) part of a marriage, but it isn't the be-all-and- end-all, is it?
I'm not going to tell anyone how often DH and I make love as we regard that as too private to discuss with others.
OP, talk to your husband honestly and kindly and work something out with him that suits you both.