'Ain' is a Scottish word meaning own. "my ain" = мой (or свой depending on the grammar, of course...), but a bit more emphatic than just 'my'

That's not a word. I think you mean "one", and the meaning there is obvious.

I'm scottish, and 'ain' means own or one. If you say, "You will be my ain true love" you saying "You will be my one true love" But usually we use it like "I'm on my ain" which means, Your on your own, thats how it's commonly used.