Finding Family by Jason Collins

LEO:

Nobody ever plans to win the lottery. But when I land the biggest jackpot in history, I know exactly where my money’s going: a private investigator to track down my biological parents and find out where I came from.
Even before Silas agrees to take my case, I know I’m in trouble. The man is smoking hot and coolly capable—my two greatest weaknesses. He’s also as determined to crack the case as I am, and before I know it, I’m falling. Hard.
One clue about my life leads to another, but the closer we get to the truth, the more complicated the investigation—and our relationship—becomes. When you dig into the past, sometimes the past digs into you, and I don’t know if Silas and I can survive the fallout.

SILAS:

From the moment I meet Leo, I can’t figure this client out. He’s filthy rich but doesn’t act like it. He’s smart but doesn’t flaunt it. He’s sexy but doesn’t seem to realize it. I take the job anyway because every PI has bills to pay.
Leo insists on joining me on the cross-country investigation—all expenses paid. He’s reliable, feels more like a partner than a client, and I respect him. In fact, I want him.
But Leo has secrets he refuses to share. The private investigator in me can’t resist, and soon I discover more about his past than I bargained for. I stumbled upon his deepest secret, and all I want is for him to trust me with it.

This is the first book in the Lottery Winners series. It can be read as a standalone with no cliffhanger.