This is entirely new, and Ronan has no idea how to deal with it. He's not a virgin, but this sensation is unimaginable to him, because he so rarely lets himself think anything much beyond blow jobs and hurried sex. That's most of what he's done. This is intimate, but it's also...with Frank. This isn't like it would be with Adam or Draco or even Kavinsky. 

The noise he makes is just as obscene, maybe somewhat desperate.

I want to take you apart, Frank says to him, and that's halfway to the goal.

"I won't," he promises and means it. He's not entirely sure he can keep that promise, because he already feels like he's not entirely in control of his body here.