Billy's eyes darted up to try and look at Frank when fingers went through his hair. It's enough to have him give a quiet moan around Frank as he draws him deeper into his mouth. Cheeks hollow out around Frank as one of his hands trail down over a thigh, kneading into muscle absently.

Even if he wasn't in the direct line of sight, there was still that thrill of excitement, of someone catching them going through him. More than that, there was how Frank looked above him, how he sounded. There's an even bigger thrill at knowing he's the one drawing out all these noises.