There is a real danger dh and d I could have ended up like this. We're both introverts, with full on jobs. We sleep separately through necessity (snoring).
I make constant efforts to maintain the marriage though. Because I love him, and want to make him happy. And he's the same. So we've both made a conscious effort to maintain rapport and closeness. In my case i try to maintain my sex drive at least to do it once per week. I enjoy it once it's underway, but not gonna lie, it would be easy to let it slip.
I arrange little mini-breaks away in the UK every so often. Nothing expensive, just an Airbnb for a night. It forces us to spend time focused on each other.
I make sure I talk to him when he gets back from work amd vice versa, plus before and after any activities, before bed.
So companionship and sex, basically.
My theory is that unless we do this, one of us will meet someone else whom we have a rapport with, then the excitement of that will break up the marriage. But then after the honeymoon period, it would just end up being a sad end to a great marriage and lifelong friendship. Plus financially ruinous.
This is all sounding very pragmatic, isn't it? But it's romantic too in the effort we put in. I love him to bits.