Vince is a veteran from the recent middle east wars the US has been involved in, and was honorably discharged due to mental issues -probably PTSD.
There's something terrible he witnessed -something he himself can hardly remember. He gets flashbacks about it now and then, weird nightmares. Whatever it was it made him erratic and unpredictable, and so ended his military career.
He didn't have an education, and has been unemployed or underemployed ever since his discharge a year ago. Right before he was deployed 5 years ago he had gotten married to an actual hooker who had dated him for 3 months and who had somehow convinced him that she loved him, and that she needed him, that he was her last hope, her knight in shinning armor rescuing her, etc. Truth is, she just wanted the benefits, and divorced him by mail as soon as it was legally feasible. A kid was born, which he has never met and is not even sure is his. But it might be his, and he really wishes to be a good father -except the ex won't even let him get close (she has full custody due to his PTSD issues and lack of employment). The boy is probably 4 years old now. The meager money he gets from his service goes nearly entirely to pay the woman for child support -and in fact it is not enough. But he doesn't want to give up.If he can prove to the judge that he is a good man, and that he will be a good father, he hopes he'll get custody to this child he has never seen.
And so, he badly needs money. He has entertained in his head the idea of working for the bad guys (drug dealers), but then he feels disgusted with himself for even thinking about it. He's has finally run out of friends and savings, and he doesn't want to beg. He's a desperate man with lofty ideals, and few means. The only thing he's good at is killing people -being a soldier.