Obviously none of us can give any advice worth its weight in gold without needing a thorough overview of all parts of your relationship and to-be relationship, but - and this is a very uncharacteristic thing of me to say here on Reddit - the upside to sex with one person, is that no matter what your current state is, the only way left is up.

Practice will lead to massive improvements over time till you're both extremely aware of each other's likes, dislikes, wants, needs, etc.

The only thing you need to ensure is pure, unfiltered honesty in bed.

Ofcourse, as people stay together for longer, they inevitably end up getting kinkier together, too. Just look at how many men start fancying the idea of seeing their wife with another guy.

I'm just saying, it's probably not all gonna be bad, at least not for the long run - which is the timeline that is scaring you anyway.