Break his heart, why don't you? Sure, they aren't as close with each other as they are with Ianto but he still cares about Jack, privately, reluctantly and hearing him talk like this is too depressing. Spike fakes a sigh, reaches for the bottle again. Loving someone forever isn't something most people are capable of, he understands that. There's no lecture coming.
"If that's the case, then make the most of what you got. Enjoy every minute of it and when it ends... part on good terms. Not like whatever the fuck that was yesterday."
He takes a swig, masking the raspiness in his voice with whiskey.