First Comes Marriage by Cara Dion

Their wedding was a mistake. Their marriage isn’t.

Sabrina Page is determined to build a new life in Aster Bay, one that doesn’t involve her parents’ money or her sister’s ex-fiancé, Sebastian—after all, he blames her for his being left at the altar. But that was before they had to share a hotel room in Las Vegas.
Now, Sabrina realizes the one man who’s hated her for a decade is the one man she can’t forget.
The last person Sebastian Graham should be fantasizing about is his ex’s chaotic little sister, especially when he knows she’s keeping secrets. One ill-advised scheme to make her sister jealous and a few too many margaritas later, Sabrina and Sebastian wake up in the worst situation they can imagine: Married.
Overnight, Sabrina’s heart is tied in knots, but her financial situation becomes…simpler. Without her family’s money, she needs time to get her business started, and Sebastian is willing to make this a practical arrangement.

Except, it’s hard to ignore chemistry when you’re playing house together. And with each passing day — and night — this fake marriage starts to feel all too real.
First Comes Marriageis a steamy, small town, fake relationship, forbidden romance featuring a grumpy hero, meddling octogenarians, waking up married, and a guaranteed HEA.