I think that you should determine if you are ok with having this kind of fictional relationship where you pretend to have a girlfriend but she knows that she has a sponsor. It didn't start well between you two and it hasn't improved a bit. You said that you wouldn't mind feeling used in a relationship, so I suppose the real problem for you is not that you are feeling manipulated but the fact that you can see so clearly the intention this girl has behind her manipulation. She is not doing it because of some twisted love interest or personality that she could have but purely because she likes your money and this is too obvious even for you.
Someone was mentioning in a post that every love relationship is some kind of transaction and as long as it is working for both, it's fine. You don't seem to be getting anything at all from your transaction with this girl or very little. So why don't you stop seeing her and spending on her and start investing in things that you like and could make you happy? Investing in yourself, your well-being, your hobbies is a way of investing in possible future relationships too.
Don't ever give up on yourself thinking that you could not have a genuine love relationship with someone because it simply isn't true :)