I think I abused my best friend
What do you think was so abusive?
I've been drunk and dumped her at home every other night only to come and pick her the next morning.
Even if you're drunk you don't have the right to abuse someone. If they are really your best friend then you should have thought about how you treat them and should make an effort to be nicer.
I'm sorry, it's just that she was costing me a lot of money.
You cant blame financial loos as an excuse to abuse someone. You really need to apologize and try to make up for what you did.