rongasm answered:
I think Stiles is going through a lot in that moment. He’s panicking, because his brain is moving so fast and he’s trying to figure out exactly what’s wrong and how fatal and what needs to be done and if she’s going to be okay. And he has the power to look at it logically and emotionlessly, but it’s Lydia. He’s looking at Lydia bleeding on the floor, and it’s making all of his logic fly out the window. All he sees is this girl who he has given so much to bleeding on the floor. Nothing he did matters. She still got here. She was still hurt.
I think it’s a very safe bet to say that Stiles was thinking about Lydia romantically in that moment. Because no matter how you argue it or what your opinion on it is, we have canonical evidence that Stiles very into Lydia Martin for many years of his life. So I think he was looking at her and seeing this girl who had seemed so effortlessly perfect, and now she’s lying on a floor with a hole inside of her and she’s using up her energy to /smile/ at him.
A huge part of Stiles is blaming himself. That’s a huge part of the reason he freezes up like that. He’s a man looking down at the woman he loves as she bleeds out and he couldn’t fix it for her. He couldn’t protect her from it.
Mostly, and MOST IMPORTANTLY to my shipper heart, I truly do think he’s thinking about all the things he didn’t do. The time he wasted. I think he’s realizing that he heavily hurt Lydia Martin, and he wants to take it all back. Even if he thinks what he feels for her is just friendship (I don’t think he does), nobody can deny that he hasn’t been treating her in the same way. He knows he hasn’t been giving her enough of his time and attention. That’s why he goes to visit her at the hospital. He’s not gonna do that anymore. She’s Lydia Martin and, as much as he denies it to others and himself, he’s always going to be at least a little bit in love with her.
And do you notice that, after that, we got more scenes with them talking to each other? More scenes with them spending time? Mhm.