Knot That Likely by Sierra Cassidy

It was his first time as a heat helper without supervision. And also his last.

Erik is bright-eyed and confident in his abilities to get Cindy through her heat. He’s done all the training, learned all her preferences, and even knows how to make her favorite foods. He just forgets one important thing…
Cindy is a cynical, mature omega who’s sworn off relationships. Heat helpers have always gotten her through her heats, and she assumes this time with Erik will be no exception. He’s hot, happy to do what she likes, and his charming smile makes her a little weak in the knees.

All it takes is one mistake to upend their lives forever.