...

It's a very cute story, if I remember correctly it's hasn't 30 chapters.
Yes they end up together
No they don't get divorced.
Spoilers:
His lost memory will come back the day after his return, but he will hide it so they can continue sleeping together.
He's a very shy person and he love so much, the only reason why he act cold is because he heard her say to her best friend that the perfect man is like the ML in her fictional book.
He took the book, studied it seriously and acted the way he thought was pretty like that ML.