The Imposter by Brenda Rothert

The secret to being the best man at your twin brother’s wedding to the woman you’ve been in love with since you were an awkward adolescent? There are two, actually: a solid game face and a bottle of strong whiskey.
What to do when things implode the night before the wedding and aforementioned dream girl asks you to stand in as the groom, though? Say yes, of course, and wing it. Don’t let it slip that you weren’t faking that kiss that left her dazed and breathless and definitely don’t mention that it’s no hardship at all to pretend she’s your wife for a weeklong honeymoon in Hawaii. And when you run into two of your hockey teammates at the resort, let them believe you lost your mind and married someone you’ve never even mentioned to them.
When she starts to have feelings for you, though? This part’s important—don’t, under any circumstances, confess that you’ve been in love with her for more than a decade. You’ll ruin everything.