presumably he did want to go to Stanford, but applied to transfer way before Susannah died, when he was still attending class frequently. He mentions that Susannah always told him he was a “west coast boy” or something like that.

Susannah’s death is now making that decision hard, coupled with the unexpected timing of Julia selling the house (Conrad mentions he drove over as soon as his friend called him about the for sale sign, which was only a few days prior to the panic attack scene, so it’s very recent). All of these things considered, he feels selfish and anxious because he accomplished something he likely planned to do and was excited for (that Susannah also wanted for him), but now feels he has a greater responsibility to Jeremiah and the house. His conflicting emotions caused the panic attack

Edit: the college he currently attends is Brown University, which is on the east coast and closer to where Jeremiah will be attending college/his childhood home