As I said up, I think calling a name in your difficult moments means you love that person. SW broke his "relationship" with Bum back when the incident had place, so he shouldn't have call him. Plus, SW was a sociopath, a killer, didn't need anyone, but still called his name
The author said you'll find out if sangwoo loved bum in the last chapter...
But tbh ive read but i sti dj (〜 ̄△ ̄)〜