Start with Fire
Beyond lust, the most accessible of twenty-something motivations, there has to be fire, that combustion of infatuation, challenge, exploration, surprise, fit, ease, fun, humor, and burn. I still feel the bite of when, in a nod to tradition and parental pressure, my not-yet-wife broke it off. For the ten days it took me to make that insanity temporary, my DNA ached and shrieked over not what we'd had but what was to come that had been denied. A few months later, when she forced me to laugh at myself, I knew I'd found a teacher, too, and lifetime of study was ahead. Start there.
Freedom in Commitment
Most successful art or invention is born inside constraint. What is beautiful or functional is shaped by boundaries. They say "here, but not there." Commitment is a sorting hat that crisply defines what belongs and what doesn't. Those edges are a source of freedom: they declare that you don't have to worry or consider what's outside of them. Once we were married, and it took until then, I relaxed. I no longer had to wonder every day if I'd done all of the right things to court and retain. That probably explains the ten pounds I gained within a year of our wedding, too, but it also signaled we were creating something very different, where the marriage itself became the main entity.
We were less than the halves of it.
Change is Constant
I always heard that but didn't get it. Change can just be slow or we are just slow to notice. But I am a very different man than I was thirty years ago. My wife is a different person, too. Each of us have shifted in and out of very different careers, not the least of which was active parenting. Don't expect the quo to remain status. You'll be disappointed. Plan for change.
Never give up on sex. I don't mean constant sexual availability; it's fine to say "not now." Just never say "no." Intimacy is a balm, a connector, a place of surprise. It's self-care, with help. The redirection of tension into pleasure. A heater. If you're broke, it's homemade entertainment. There is even sex that is just maintenance, necessary for those times when every other connection in a relationship is frayed, forgotten or simply unattended. Two kids under two will do that. It's no big deal if the planet shifts for one of you and there's barely a buzz for the other. In those moments when we merge bodies, we give and receive the human fundamental of touch and warmth and trust. Sometimes, especially in the tunnel that is caring for young children, work, or managing a career, that has to be enough.
By the way, it gets better when the kids leave the house and there's no possibility of having children. I cried when, after dropping off our last one at college, I walked back into the now emptier house.
An hour later, I was feeling pretty good.