Everyone knows about the "honeymoon" phase of a relationship/marriage.

That is what I mean by "intensity/passion/fire."

You can see the intensity/passion/fire of a relationship/marriage if you just look at the couple's body language and nonverbals: sometimes you see couples who have extremely high intensity/passion/fire and they just can't keep their hands off each other.

I'm sure you all know what I mean by this.

1: In a relationship/marriage, does the intensity/passion/fire ALWAYS die?

2: Do you know any couples for whom the intensity/passion/fire NEVER died?

3: And when it does die, HOW exactly does this process take place? I mean, I guess scientists could analyze the dynamics of a couple in a relationship/marriage and try to sort of monitor how the dynamics evolve (or devolve), but it's way too personal/private to allow scientists to monitor you, so it remains a mystery. I mean, we all know that on Day 5 of a relationship/marriage (in the case of a marriage, a couple would probably still be on their honeymoon) the intensity/passion/fire is usually quite high (when does it peak?). But on Day X it has usually declined a lot. But how exactly did that take place? What happened between Day 5 (or whatever) and Day X? It's just a gradual decline, right? If you were to graph the intensity/passion/fire then it just declines linearly, right? It's not like one day you wake up and suddenly the intensity/passion/fire has radically decreased; it's gradual and imperceptible. I suppose there is, however, a distinct point at which every couple has their "first fight." And I suppose that there is a distinct moment at some point at which one/both of the people in the relationship/marriage realizes that "I'm not happy anymore"; it's sort of like one day you check the scale and you're 50 pounds overweight...scientifically you know that it was a gradual process but the realization is sudden because you were blind to the process and not analyzing it properly.

4: How exactly do marriages actually devolve to the point where it gets so miserable that divorce is necessary? It's shocking to contemplate that a couple that was so in love that they decided to tie the knot actually, somehow, reaches a point where not only has the intensity/passion/fire declined but they are actually miserable in each other's company; that's is so mysterious/bizarre/shocking to me. How does that devolution actually unfold? It's disturbing as well as mysterious to me. It's so sad. There are so many miserable couples and I would love to know the exact process by which things devolved and how exactly things got that way from the starting point of being madly in love.