He hand on his ass went straight to John's cock, with a pulse of heat that made his head spin, his grip on Ben tighten, and a soft growl that got lost in the intensity and slight roughness of returning Ben's kiss. Give him a second and he'd get to that rocking - or doing more than holding on, and kissing and feeling the weight and heat.
John wasn't thinking about impotence. He was realizing that for all his pushing at Ben... he'd forgotten, or tried to, how much he'd been wanting and needing and trying really hard to ignore as more than...the sparring and pushing and challenging.