In the building where Gabriel and Constantine spoke, he expressed his dismay that he has not repaid his debt to God to which Gabriel replies,
You are going to die young because you smoked 30 cigarettes a day since you were 15... and you're going to go to hell because of the life you took.
Who is Gabriel referring to? The only instance I could think of is Gabriel referring to Constantine himself when he was talking to the doctor
You saved me before, you can do it again, right?