[ This is a terrible idea and he knows it but what would his life be without a few terrible ideas? It could practically be his middle name at this point and as far as decisions go, keeping up with this kiss isn't the worst he's ever made. He's not too keen on being dragged into the middle of Jack and Ianto here but what the hell is he supposed to do about it? Isolate himself from two of the very few people he can actually stand?
Letting instinct take over fully, Spike growls into the kiss, his hands finding their way to Jack's hips. Let's see how far this'll go. ]