There is someone that I love and care about a lot that keeps asking to borrow money. I know what they want the money for and it's not good, but I still give it to them. I don't understand why I keep giving it to them. I yell and cry about it, but in te long run I still do it. What's wrong with me? Why do I keep giving it to them?

Do they pay you back?
Do they care if lending them money leaves you short?

Ask yourself questions that make the problem more real to you.
Like if they aren't caring that they leave you running out of money then you should realize that you shouldn't care that you don't lend them money for drugs or whatever it is they are wanting it for.
I have also learned that when I don't help others out they always manage to come up with another solution or person to help them with what they want so badly.
You need to get firm and put your foot down but first you need to get serious with yourself. As long as you are easy going you are going to give in.

You love the person and would do anything that person wanted. If the person wants money you give it. If the person wants love, you give that. Maybe he doesn't want your love, just your money. Maybe you just want his love and not your money.
If you keep giving the alcoholic a drink, are you strong enough to take his keys? If he drives drunk, do you think the bartender is responsible if someone gets killed?