Realising what he'd said, Severus turned his face away and tried to retract his hand, but then hers was atop his and he couldn't stop holding onto her. Slowly dragging his gaze back to watch her, he could only nod while he formulated his words. Anything that sounded coherent and light; he didn't want to ruin the moment either, but there was so much hurt, just so much anger between them that he didn't know how to go on. And when she mentioned Professor Slughorn, he knew what to say.
"Thank you for bringing me here. I may not have made it much longer if you hadn't." His soft tone belied the warring emotions within. Did he want to be here right now? Not too long ago, he realised that he was welcoming of death, but now that he was lying here, with Lily looking at him not with animosity, but with compassion, he couldn't feel even more different than before. All he'd really wanted was to get Lily back. He'd tried so hard, and was brushed off just like that. He simply couldn't hold back what he really wanted to say.
"Lily... I'm sorry. You know I'm so sorry for everything. I couldn't live knowing that I would never have you back in my life..." There, he'd said it, and he felt a little wave of relief passing through his core. The knots in his stomach released a fraction of their tense hold. If Lily wouldn't tell him to sod off right there, they might actually get someplace with their lost friendship.