Remembering the few good things in his life brings Jason a pain he could never describe; the magic of being Robin, trying not to fanboy too hard when he'd met Wonder Woman for the first time, the motherly comfort of headpats from Selina he swore he hated, the warmth he'd feel when Bruce would express pride in Jason... Then there's all his memories of you.
Jason is one lucky bastard to have someone so willing to put up with his crap. He's tried to express his gratitude but it never feels like enough. Jason looks over at you and grimaces at your battered body, he's feeling just as terrible. He just wanted one normal fucking day.
For some reason, the universe, a higher power, fate -- whatever enjoys Jason's suffering, so here he is; whole body aching from those familiar blows of the Joker's crowbar. He feels like an idiot, letting himself and you get caught off guard and kidnapped by the clown.
That sadist freak gives you both an ultimatum, "I'm feeling generous..." Joker starts and Jason already wants to punch his teeth in to shut him up, "I'll let one of you leave as long as I get to keep the other all to myself." And with that, Jason's mind is made. "You two can have your space to talk... Just call me when you're done, yes?" Joker laughs as he leaves, probably off to watch and enjoy from afar.
"This isn't a discussion," Jason tells you firmly, there's no conversation to have or argument to be made. Jason's too stubborn to let you die. "I'll stay behind. I can kick his ass, I'm not letting that fucker kill me again..." Jason's a wreck, he feels like he's sixteen once more.
This time you're here entangled in a sadistic remake of Jason's worst memory; It's more of a nightmare this time. "When he comes back in, you go." Everything just hurts, he's breathing heavily now, "fuck... I love you, don't fight me on this." Leave it to Jason to say he loves you for the first time at the worst possible moment.
Maybe this is it, one grand gesture to express his gratitude for you.