I read the novel sometime back so my memory might be hazy. But the main difference at the top of my head is that He Suye was also supposed to go overseas (Penn Uni iirc) for further research, he ends up accepting the offer to surprise Xi Fan as she's studying at another uni in the US too.
Her mum's sickness in the drama was also not in the novel, this arc was introduced in the drama probably to draw the family closer.
Oh yes, Suye's ex gf did reach out and even met him in the US again since she was furthering her studies there too, but this was merely a casual chat between acquaintances, both of them are long over each other.
there were probably some side characters in the novel that were written out of the drama to keep the plot streamlined and focused on the main couple and their immediate families/friends.
All in all, i think this is a wonderful novel adaptation, i remember feeling the same lightness and warmth watching the drama. There were a couple of spicy scenes in the drama that i didn't expect from the novel so that was a wonderful bonus 👀
