Here are some points:
They're both from Macon.
In the comic books, Glenn ocasionally says he had financial issues before the apocalypse, saying that he was broken and all.
Vince kills a guy and goes to jail for "helping his little brother*. EDIT: Also, before dying, the guy said "I don't even know your brother."
- The guy who Vince killed could be someone charging Glenn and threatening him, so Vince took care of him to help his family.
What do you all think?