I am in love with my ex, but he is dating my best friend, He still loves me and he wants us to come back together.

Please explain. This makes no sense as you wrote it. Is your best friend holding a gun to his head?

Your ex is probably playing both of you. You just have to wait until he finishes using your best friend,and he may come back to use you.

If he wanted you back together, he would be back with you. He is with who he wants to be with... for the time being.

As another answer said, why doesn't he come back to you? How do you know he still loves you? Has he told you? If so, then why is he with your best friend.
I would forget about this person, and make some new friends, including a best friend. Good luck.

I suspected your admitted addiction to drugs is a large part of your problems with your ex, your best friend and whatever else is going on.