Collate this same information, encrypt it and then use [a key sharing algorithm](https://en.m.wikipedia.org/wiki/Shamir%27s_Secret_Sharing) to split this encryption key across a set of semi-trusted contacts.

Those friendships might outlive any romantic partnership I do have in future. So I don't think it has to be a partner specifically. Of course, there are still some things that you might not share as openly even with that trust in place, but that doesn't stop you from having a backup plan.

If you have family, extremely close friends (as adults, life-long friends), these can be options. Consider keeping your 'binder' in a safe deposit box and setting up access via your bank.

If not, an attorney or even CPA may be able to keep this information for you.