Chemistry is
I agree with Kelly Eden, a relationship without chemistry isn't great. I've been together with my wife long enough that the infatuation phase is a distant memory. The chemisty is definitely still there.
Everyone has their type: physically, emotionally, intellectually. My wife is one of the top 3 physically attractive (for me) women that I've personally met in my not so short life.
That chemistry helps a lot when you're stuck on the next weeks-long lockdown due to Covid. Or one of us is cranky after a tense phone call. Or we just want to snuggle in bed a couple minutes after the alarm rang at 5:30.
I have had many platonic girl friends. I have never had it work out romantically if the chemistry wasn't there. Maybe that is just me. I’m a very physical person.