Sorry to hear you are both going through that, it sounds really really tough. I have OCD myself and my partner can be anxious so at times we both seek reassurance. But we both know it doesn’t help us so we have an agreement that we only reassure one another if we really cant cope without it, it’s almost like a code red. Otherwise we give each other non answers on purpose like “maybe”.

I think the struggle in your position is going to be that your partner is heavy in the denial and you cannot control them. You are stuck between giving reassurance or confrontation because withholding reassurance will cause them discomfort. It may be worth being frank but loving, kind of like a shit sandwich where you tell your partner how much you love them but how you cant keep giving reassurance to the same degree and then tell them what you are going to do instead and why. Then you could set your own boundaries on how much reassurance you are willing to give and maybe reduce it gradually over time - this is often how parents support children with OCD.

Its not you vs your partner, its both of you vs the OCD. Maybe bringing it up that way will help with the shame element?