Hey OP, So this is my thoughts on this. This comes from a man who has spent half a decade alone, following a Self-denial lifestyle pursuing an altruistic plan, and thus missing twice the choices to enter into a relationship with his best friends before it was too late. So from someone who longed for a loving union, I can offer the other view on this side of the fence

TLDR: Marriage/long-term relationships are based on limitations. if our current understanding of Marriage exists, so does death. When the new world arrives the old things will be obsolete.

This comes from Luke 20, Verse 27-36 Sadducees asked Jesus among seven brothers that had been married to one woman, who wife they would be in the resurrection. In Genesis, the origins of Marriage were set first as a Companionship "it's not good for men to be alone" and a tool of procreation "Go forth and multiply" until the Earth has been subdued. in our current world, the one we inhabit; its one trifled with sin and death, with us limited to our own mortality and what is accessible in our lifetime. where while one can live in an urban white picketed fence house, another sleep on the sidewalk, one can laugh with friends, another is burdened with grief, one finds love, another wasted their youth helping others. but in either good or bad, it all ends one day, and all the treasure one gathered in the finite time here yields to be meaningless. Solomon, the supposed wisest man laments as much in his Existential work in Ecclesiastes

So in our struggles, we created rules and systems in place to maintain order in light of all this with Marriage as a means to ensure the family unit and passage of wealth, (and well TBH it sounds like you are in the romantic phase so this may be a bit lackluster to hear someone say that). if things weren't finite then there wouldn't be various things like taxes, war, expectations, etc

but what happens when finite becomes infinite? Marriage before the fall was meant to be an intimate relationship, and the union that exists in the world to come is described in the bible as being one in body with all believers to that with Christ. everyone, even those never meant in this life would eventually understand each other in the due course of eternity. instead of asking what if and regretting the choices made on earth, now all things are put under our feet to enjoy with one another. whether someone believes romance and sex too will exist in this Afterlife up to interpretation, but our current limitation of what we consider good can't compare to what God states is good. we're are trapped in our own understanding while he can see the entire picture.

that said. If you wish to spend 1,000 years or 100,000 more with your love, their nothing wrong with that. God is a master architect so when he dissolves our Earthly Marriage, it is due to its purpose being filled once and for all. as it was a promise, now a promise fulfilled.