Stefan knows that he should be trying to figure out away to break out of this steel box, but all he can think of is Bonnie.
The moment Silas revealed Bonnie's death to Stefan; his first thought after the despair that shot through him had been that he should have known something was wrong. He should have seen the signs, pressed her for the truth.
He thought something had been up with when she dragged him to the utility closet right before graduation. He came to the school early anxious to see her. When he finally did see her, he'd barely gotten one word out before her lips were on his, her legs were wrapped around his waist and he'd been inside of her.
Not exactly unusual for them these days (they make time for rendezvous whenever they can), but now he remembers that she seemed strangely subdued as he was thrusting into her wet heat. It was as if she had been savoring the moment.
At one point he even asked if something was wrong, but instead of answering she clenched her walls around his shaft in a way that had his eyes rolling in the back of his head and bit into his neck. After that he hadn't been thinking about anything other than bringing them both to climax.
By the time they were finished, they had been running slightly late and any thoughts of something being wrong had completely fled his mind.
And that had been the last time he'd had any significant moments with her other than the group hug they shared right before the ceremony.
Eventually he grows exhausted of replaying that fateful day and instead focuses on the moment his feelings for her began to change.
He and Bonnie had grown closer in the last six months, becoming better friends. It wasn't until a couple of months ago that their relationship started to shift into something more.
The shift began after the situation with the witches; he had been trying to get her through the pain of reliving Jeremy's death. They had been locked in a hug when she suddenly pulled him into a kiss. The kiss immediately grew passionate and it wasn't until she was trying to lift his shirt over his head that he came to his senses.
He resisted at first (despite being hard as rock) because he knew she was vulnerable and he hadn't wanted to take advantage of her, but when he had taken a look into her pain-filled eyes, he could tell it was something she needed. And truth be told after the last year, it had been something he needed as well. So when she made another attempt to take off his shirt, he let her.
Afterwards, she asked him to leave, insistent that what happened between them was a onetime thing and should be kept between them. He agreed and when he talked to Damon later on, he acted as if nothing unusual had happened.
Of course it hadn't been a onetime thing.
A few days later he'd gone to check up on her and once again one thing led to another. Hours later, he woke up in her bed, his body aching pleasantly, and Bonnie in his arms.
After that, him coming to check on her became a ritual. Sometimes those visits ended with them tangled together in her bed (or her sofa, and once they had been impatient and gone at on the stairs), but more often than not, they would find themselves content with just talking.
She would talk about her struggle with dark magic and he sympathized by mentioning his own struggle with darkness. They commiserated over their failed relationships; the feelings of betrayal they both felt when they realized their exes had feelings someone else.
Before long, prom came around the corner. They had discussed going together, but knew it would cause problems with their friends and instead decided to they would fall back into the roles that were expected of them.
Naturally the night was a disaster and ended in Bonnie nearly killing Elena after nearly being killed herself. He and Damon managed to talk her down and when he asked her if she was okay (a stupid question, but it was the only thing he could think to ask at the time), she stalked away angry.
He'd gone after her immediately, ignoring the perplexed look Damon gave him. When he got to her house she had been furious and initially she hadn't been very receptive to his visit. He even got thrown across the room for his effort. But he eventually wore her down and he stayed the night.
Later on as he watched her sleep, he came to conclusion that something needed to be done about Elena's humanity. He's sure that to ever one else his one-track focus on flipping her switch had been for Elena's sake, but he'd really been afraid the next time she and Bonnie had a confrontation, one of them might not come back alive.
By the time they reached graduation day, Elena's humanity had been turned back on, but they had to deal with a host of other problems. That left them with very little time together and he actually planned on asking her to go away with him for the summer when he had been attacked by Silas.
Now he's trapped in a steel box with no chance of being rescued and without Bonnie he's unsure if he even wants to be rescued.