Don’t give this guy another dime he sounds creepy as hell. You don’t have to have an excuse to not give someone your money if they ask for it, so never feel pressured or like you couldn’t say no. If you say no and he asks why tell him it’s literally none of his business cause it isn’t
Definitely isn't being selfish. From your original post I think it's clear that you do have a heart that wants to help, it isn't selfish or mean to draw a line at some point, especially if you don't feel comfortable with the situation. If you were close friends (which I don't get the idea you are from your original post) and you knew his situation I could understand that you might feel that way inclined, but you shouldn't feel like you have an obligation. If he asks again, tell him either that you aren't in a position to keep lending money - whether you are or not, it's not his business - or just that you don't want to keep lending money. If he keeps bothering you about it after that, you should talk to a manager or supervisor about it because it is harassment if it makes you feel uncomfortable, you have the right to feel safe while at work. If he does "make your life hell" as a result, same thing goes. Bullying and harassment in the workplace isn't tolerated these days.
No! You're not selfish at all, there's a lot of takers in this world, and as you can clearly see by the way he did it that he's just trying to get more and more from you. I've always refused to lend out money, unless it's someone very close to me, the only co-worker I ever lent money to was when I was still living at home not paying bills or anything, and she asked for a nice chunk of money, which honestly other people would probably throw red flags up over, but I lent her the money because I had known her for 2 years and was really close with her and her family at that point, and she paid me back out of her last check. But it wasn't like she did it constantly. Really all you can do is cut them off. In your position I would just tell him flat out that you're not comfortable lending out money anymore. If it's constantly like that, he has some issues and needs to keep better track of his own money.