It's in His Kiss by Jill Shalvis

she watched in pleasure and fascination as the muscles in his abs jerked. She wasn’t too sure of her skills in this arena, but he looked good enough to lick. So she did. And then again.
    And then she took him into her mouth.
    He made a low, rough noise, and she looked up at him through her lashes. His head was tipped back, eyes closed, the water flowing over his face and down his chest. His fingers slid in her hair and held on. She tensed, but his hold remained gentle, not guiding or pushing her. It was more like he needed the grip just to hold on, which actually made her feel powerful, and sexy. So sexy . . .
    All good signs, she figured, and continued on, absorbing the groan that came from above her and echoed against the tiled walls when she experimented a little bit.
    “Sweet Jesus,” he muttered, his body as tense as atightly coiled spring ready to snap. After a few moments, he swore and roughly hauled her up.
    “What’s wrong?” she asked.
    Nuzzling his face in her neck, he shook his head. “Gotta slow down or I’m gonna come.”
    “Wouldn’t that be only fair?”
    He groaned again, kissed her, and then said against her lips as he hoisted her up, “I want to be inside you when I come, when we
both
come.”
    The words nearly sent her up in flames, but she needed to tell him—
    “Hold on to me,” he said. Leaning her into the tile wall, he slapped a hand out for the condom. “Magnum blueberry,” he read with a lip twitch.
    She’d had her hands around him. And her lips. So she was speaking on good authority. “At least the size is right.”
    He snorted and, holding her pinned against the wall, seared his mouth to hers. She parted her lips for him and garnered herself a low, sexy growl from the back of Sam’s throat as their tongues touched. She’d been doing her best to stay lost in his gaze, in his kisses and touches, and not let Real Life intercede, but she still had to tell him. “Sam.”
    He sucked at the sweet spot right beneath her ear and her eyes nearly crossed in ecstasy. “Sam,” she said again, but he wasn’t listening. She tapped his chest. “Sam, I need to—”
    “Anything,” he murmured and kept kissing her, his hot mouth robbing her of cognitive thought.
    “I—” She blinked. “Anything? You can’t offer me anything.”
    “Why not?”
    She paused and appeared to process this question very seriously. “Well. . .I could take advantage for one.”
    “Go for it,” he said hotly, letting out a slow, absolutely wicked bad-boy smile. “Just remember, paybacks are a bitch.”
    She shivered, not in fear but in arousal. Good Lord, he was potent. “I’m trying to tell you something.”
    “Okay, babe,” he murmured, and kissed his way along her jaw toward her mouth. “You tell me whatever you want while I—”
    “Sam!”
    At the seriousness in her voice, he again lifted his head, giving her his full attention. Which she’d totally and completely underestimated, because Sam’s full attention made it difficult if not impossible to think. “I don’t want to disappoint you, but—”
    “Becca.” His features immediately softened. “You won’t. You couldn’t—”
    “I won’t come with you inside me,” she blurted out.
    He went still for a beat. “No?”
    “I. . .can’t.” Oh, God, this was embarrassing. Why had she thought this a good idea? She should have faked it. But she wasn’t good at faking it. “I want to, I try to, but it just doesn’t happen for me. And sometimes that can be . . . upsetting for a guy, I know, and I just really don’t want you to be upset.”
    Something passed across his eyes, and it wasn’t pity or she’d have shriveled into a tiny ball and died. She couldn’t put her finger on it because he kissed her, softly at first, then not so softly, and before she knew it she was panting for air and whimpering with need, gripping him like he was her lifeline.
    “Becca.”
    “Huh?” she asked dimly.
    “Open your eyes.”
    She did with