Lyra's strike narrowly had missed Sorren's heart, sparing his life. This left Sorren with the idea that Lyra still harbored some kindness for him, thinking she had intentionally let him live.
So, when he found out that Lyra was safe, he decided to return.
Even though she had left him stranded in Snowfall for months, Sorren believed Lyra still saw some value in him. Maybe, he thought, she'd let him back in, and they could start making money together again.
"Sorren, why'd you come back after she cut you loose?" Morrison asked, arms folded as he sized him up.
Sorren, full of confidence, replied, "Why else? I'm her right-hand man!"
"Not anymore, you're not."
Right then, someone interrupted to ask Morrison what to do with some old equipment. Without much thought, he said, "Toss it."
That pushed Sorren over the edge. He shoved Morrison hard against the wall. "You stole my spot!"
Morrison just chuckled, easily brushing him off.