Well, they can married, if I remember correctly MC's grandma was opposed to her relationship with Ren. Ren's family was very very supportive of their relationship. She gets pregnant and they have twins,Ren becomes a doctor. They are very happy to have made a family but she's still loosing motion in her legs and other parts. So it's clear that she won't be able to see her twins into their teens bit they are pretty happy.

Just finished reading this, I cried from chapter 18 till 37 (end) it was beautifully painful for me at least. I read it in spanish.
https://tmofans.com/library/manga/18805/10-manbun-no-1
Spoilers:
It's not a "and they lived happily ever after" it was more like they kept living even though of everything. They register their marriage while still in school, she manages to graduate, she wants to give birth to Ren's children he agrees. They celebrate the marriage ceremony, a while later she finds out she's pregnant. Two healthy boy and girl are born. She's still slowly loosing her body's movements. But when you have a damn good husband, damn good best friend and damn good famil yand in laws then even hell can't hurt you enough to steal the happiness that you've earned. I loved it.