First Love, Second Chance by Vesper Young

Lucas:
I’ve regretted leaving her every day for ten years. She convinced me to follow my dreams, move across the country, and found a tech empire worth billions.
Well, I did that. And none of it compared to having Kara in my arms.
A twist of fate puts Kara back in my life, and I’m not going to let this chance go. I’ve never wanted anyone more. Her smile, her laugh, I need them like I need to breathe. I can’t resist her, and I don’t want to.
The only problem: she refuses to let me back in her heart.
That’s not an option. And I’ll do anything to prove it to her.

Kara:
Luke’s crashed back into my life, and I’m anything but ready. When he left ten years ago, my heart shattered into a million pieces. First loves do that, don’t they? I’ve spent the past years duct-taping it back together. Then I built a wall around my feelings so it won’t happen again.
Now he’s here. I can’t deny the connection we have. I convinced myself it was young love, but even now, just one look in his eyes and I know it was real.
I want him. I want him more than I ever have before.
But I can’t give in. I have to fight it, for a dozen reasons. He’s my ex. He’s my boss. When he left, it broke me—how can I ever risk that again?
Oh, right, and the biggest reason.
I never told him we have a son.