Stiles knew he shouldn't take Derek's harsh words personally but he did and it caused the human to clench his jaw tight. Not only was he screwing up his relationship with Derek but he was now also screwing up Allison's relationship with him.
"Sorry," Stiles said speaking to Allison because it was clear this was his fault. He should have knocked or known Derek would be in bed with Allison. Stiles hadn't slept the night before and he wasn't thinking clearly. "Tell Derek to stay. We can talk later."