We caught up with the singer-songwriter at The Grove in Los Angeles Thursday ... and he made his feelings pretty clear ... consenting adults should do whatever the hell they want in their love lives without government interference.

That said, Ne-Yo says he's not going to Washington, D.C. to fight for a law change ... 'cause it's not currently affecting his personal life, and he's not sure he wants to marry multiple women.

We also asked Ne-Yo why he doesn't write songs about dating multiple women ... and, he says it's 'cause he draws on his own life experiences, and this is his first relationship with two women.

And, we even asked Ne-Yo's GFs if they're interested in walking down the aisle together to marry the star ... and, ya gotta see their reactions to the question.

Ne-Yo enjoying a polygamous relationship ain't new ... remember, we told you Ne-Yo was spotted down in Miami holding hands with two women last summer -- after his divorce from ex-wife, Crystal Renay.

The two split in part because of Ne-Yo's infidelity ... and, it seems a relationship with two women may suit him better than a relationship with just one.