At this point, spent is just about Jack's only aim too, and he doesn't care how he gets there either. Once they've done this, once they've cleared the air, so to speak, then perhaps they can get down to something more refined, but for now? He really doesn't care.
Not for the first time in his life, he finds the fact that he wears both braces and belt on his trousers more than a little frustrating when Spike goes for his fly, but there's enough leeway at least to get his pants open, and nothing underneath them to obstruct access to his hard, hard cock. In a minute, perhaps he'll try and roll them over so he can get his coat off, get a few more things off, but right now there's cool skin making contact with his cock for the first time and that has him crying out into the kiss and bucking hard into Spike's hand.
His fingernails dig into Spike's bare back as another jolt of want surges through him, and he bites into the kiss, needing the harshness, the violence, to counteract the sheer exquisiteness of what's happening down below.