Chocolate Secret by Maxine Henri

Once he saw her, he couldn’t get her out of his mind. The only woman he can’t have.
Phillip Turner is a rich recluse with a dangerous hobby. He steals art. When he decides—out of boredom—to take one last client, the mission turns out too personal. One last heist. He has more than enough money, but it’s the thrill he’s missing.
One last heist. Nothing can go wrong. Only he gets caught. An enigmatic woman walks in on him and then shocks him when she leaves. Just like that. No questions. No drama.
He should be concerned. Instead, he gets obsessed. He is the intruder, but Lena Arnolds takes his heart. Or at least his sanity. He can have any woman, but he lusts after the one who belongs to another.
Until she doesn’t.
Lena might be finally free of her abusive husband, but will she ever trust Phillip with her heart? After all, she knows him only as a thief.

This is the last in the Untamed Billionaire series, but it can be read as a standalone.