If Spike hadn't bitten so deep, if he thought he could move either hand from where it's clinging desperately onto Spike's shoulders without his knees buckling, he'd be attempting to return the favour of what Spike's doing to his cock, but as it is he's already too far gone and he knows this isn't going to take long, in either respect. He can feel the growing numbness in his extremities and the growing dizziness in his head, and and he's helpless between Spike's mouth and Spike's hand, one bringing pain, the other pleasure, mixing in an exquisite combination that's coiling and pooling deep inside him, just about ready to explode. And this time, there's no reason to hold back, no reason not to let it come, and so he does, mouth open on a shout he doesn't have the breath for and so is silent, convulsing violently in Spike's grip as he showers his hand with come and his mouth with his blood.