Let's face it, concubine usually expresses a less-than-equal relationship of power in favour of the man. The reverse situation would be toy-boy or live-in-lover, though personally I'd have no objection to male concubine.
This thread does not contain sufficient context for a productive discussion, and is now closed.
It's possible that the original poster would have better results by posting the Polish term in the Polish forum. People who understand the use and connotations of the Polish term may be better able to help in translating it into English.