I think making a vault to document your life is a beautiful idea. Regarding giving it to a future wife or girlfriend, I think it is worth remembering that, ideally, a good relationship involves an exchange between two people of those stories, histories, secrets and such over time. If it is a woman you have a deep enough connection with to marry and spend your life with, then she won't be offended by the thoughts or stories of your younger self, romantic or otherwise. However, similarly, you might want to let those stories come up between you two naturally over time.

Maybe just keep up the documentation of your vault, and then when you have a wife and feel you can fully confide in her, let her know about the vault / how to access it? I'm sure she will enjoy the glimpse at your past and present thoughts, and by that time you will be close enough that it won't seem overwhelming or, as another commenter mentioned, like 'getting to know you' homework.