YA/NA where heroine is a waitress (?) and hero is in college and heroine doesn't know how to read

[Penn]

I read this book where hero is in college and heroine is a waitress. I think I read it around 2020-2021. They were the same age, it's just that heroine had to work because she's poor and also an orphan (?). The heroine doesn't know how to read and hero taught her. They were really sweet. I think the hero also nicknamed her "Sunny". But then for some reason, heroine had to leave and just wrote a letter to hero. Hero was heartbroken.

A few years later, they meet again. Hero became a jerk. Heroine actually had a child with hero but did not want to tell him because she thought it would get in the way of his future. That is all I can remember.

I hope we can find the title of the book!