Spock hesitates again... He can't help it, he's a creature of habit and he has to make sure.
But then he looks into Jim's face and sees hope. Perhaps they do have a chance... he just doesn't want Jim to run away from him, to leave. To die. The Vulcan shudders as he places an almost desperate kiss to Jim's lips.

He doesn't answer as the world dissolves around them, leaving them once again in Spock's room, the Vulcan practically in Jim's lap as he continues to kiss away.
Every kiss has the same message, over and over again 'never leave me again.'