The Hero and heroine were high school sweethearts but it's said early on they broke up as he cheated but there seems more too it.
Circumstances mean they are spending time together.

During separation, 12 years.
Hero 'Even when you're with other women, you're never really with them."
"That's not true," he said, frowning at his brother's analysis of his love life.'

There is also a conversation to show the heroine had relationships, one lasted a year.

It was a bit frustrating as the facts of the cheating incident are not known to the reader or the heroine, which is kept til the end.
HEA.


Details of cheating.

Around Prom he witnessed his father doing something that was bad and he got drunk and had sex with another girl then to not have to explain or reveal his father's sordid secret he made light of his relationship with the heroine making her believe they weren't special.
There are no intimate scenes of the cheating, just that it happened. ( )