This sentence is somewhat colloquial, and probably more acceptable in American English. British English speakers would be more likely to say 'I have always done the right thing by you'. Or you could turn that around and say "I have never wronged you', although that is slightly literary and not common in every day speech.

I've always been kind to you. (Do you mean something like that? ) After By you need to use object of passive form.

From an online dictionary: to deal with someone in a kind way, as you should He always did right by his children.

I must admit I would use this, but then I'm a bit archaic. It means that you have always treated me fairly, perhaps even generously.