As long as the ring is not stolen which is a completely different issue. Tell your cousin to chill. Its a teenage fling that'll burn in flames & end soon. Yeah if the kid is getting physically involved I would worry then as well. Again if he already has a 19 year old sister who is fine then no one else should worry.
Kid probably goes to high school. Sees everyone having girl friends/boyfriends. We can't expect kids these days to have crushes the way we used to have back in the days.
And you can easily find a gold ring for any where around 25 bucks & I am talking about real gold here.