Although you love your husband, and obviously he loves you, to tell him that you no longer wish to have sex with him, will hurt him deeply; and he will wonder why.
As the years pass, desire does diminish. The every day of early marriage will give become once a week when you are seventy. Unless it is very painful for you because of dryness, atrophy, rheumatism or whatever, my advice is don't stop.
Explain your feelings to him.
If it seems to have become boring, than you can buy books that will give you ideas. You can try new things, times, places positions, so that you both feel a thrill.
If all else fails, do devote time to kissing, cuddling, fondling and displays of affection and your body, to show that you love him.
Turning off the tap could be disastrous for both of you.
In any case, sex is good for you, mentally and physically, and can help delay the onset of dementia.