While you wait here are some name and why I picked them
1. Until You Chose Me
This title captures the central theme of your story.
From the beginning, Boun's goal has never been simply to "end up" with Prem. Even after Prem becomes pregnant, Boun refuses to use the pregnancy as a reason to confess or propose. He waits because he wants Prem to choose him freely.
Every major event in the story points back to that idea:
Boun has loved Prem for years.
He takes care of Prem without expecting anything in return.
He hides the engagement ring.
He carries around plans for their future but never pressures Prem.
He proposes only after Prem says he loves him.
2. Why Did You Choose Me?
This title stays closest to your original title, Why Did You Marry Me?
Instead of asking about marriage, it asks the question Prem has been asking himself all along.
Throughout the story, Prem constantly wonders:
Why does Boun always wait for me?
Why does he remember everything about me?
Why does he take care of me?
Why me?
Eventually, the answer becomes clear.
Because Boun loved him long before the pregnancy.
3. The Long Way to Us
This title focuses on the journey rather than the destination.
Your story isn't a quick romance.
It's years of:
friendship,
hidden feelings,
misunderstandings,
jealousy,
pregnancy,
emotional growth,
learning to communicate,
and finally choosing one another.
"The Long Way to Us" tells readers they're about to experience a slow-burn romance where every chapter brings the characters closer together.