I'm just guessing here but I have seen some ads about medical creams that should help with dryness and thin membranes down there. Some contain lactic acid and some contain hormones. I have no idea if they would work for you but you could investigate and ask your doctor if you can try them. They were mentioned at one Finnish arthritis site about Sjögren's disease but how much the products can help wasnt mentioned. The site also got me wondering about support organizations where you live, could they offer discussion groups or something for you?
Anyway, dont put yourself trough needlessly painful experiences, I bet your relationship has many other things you both can enjoy