I think the determination of your role in D/s is an awful lot like sexual orientation. It is a compass, but not a roadmap.

With orientation, just because you are heterosexual doesn't automatically make you a good lover, or boyfriend/girlfriend, or spouse. You have to work at all of those things. Same situation if you are gay or bi. Just because you are inherently a Domme, doesn't mean you aren't going to have a lot of work to do.

I think that D/s roles are determined either at birth or sometime in childhood. I say this because I know many people that have tried different roles before they fell into the one that just feels right. It's the "coming home" feeling.

Also, although I would consider myself a sub by "nature" I was definitely "nurtured" to be much more Dommely. So sometimes I have to work quite hard at my submission.

A 24/7 relationship is a very substantial undertaking. There are going to be some rough patches. That is completely normal, and doesn't make either of you a failure. If you are both committed, willing to put in the hard work, and keep the lines of communication should be to work through it all.

I wish the best of luck to both of you.