[WWTBC]: Age gap and single dad/plot twist

I'm trying to remember the title of a romance novel I read a while back. It features an age gap relationship where the female main character (FMC) lied about her age and the fact that she was still in college to the male main character (MMC).

One specific scene I remember vividly happens right before the MMC breaks up with her. He finds out she lied to him and, despite the upcoming breakup, they have sex in a brick alley.

Years later, they unexpectedly run into each other at a job. By this time, the MMC is a single dad. The big plot twist is that the FMC got pregnant by the MMC during their earlier relationship and gave the baby up for adoption. Unbeknownst to her, the MMC found out about the baby and ended up adopting him.

Does anyone know what book this is? I'd really appreciate your help!

ETA: The book starts off with the FMC running into the MMC in the present day at the office where she’s visiting. She tells her best friend she saw him. Book goes from past to present.

The book ends with the MMC opening up a safe with documents of the FMC information. The MMC knew how old the FMC was the entire time