No offence, but he doesn’t deserve your courtesy. I’d understand if he gave back the necklace, at that point I’d just ignore him. But the fact he hasn’t is the kicker. Yeah, it’s a dick move to lie to someone like that, but it’s an even bigger dick move to take a gift that was worth a lot to them when you have nothing towards them what so ever.

You need to turn people against him if he’s not going to give the necklace back. Start simple. Ask for it. It’s the least he could do for that he’s done to you. If he refuses? That’s when you hurt his reputation. Let the whole school know just how much of a scumbag he is. If you can, get proof of it. Tell everyone he basically robbed you, as that gift isn’t meant for him anymore.

Don’t let him push you around over this. From the looks of it he has no intention of apologising. In his mind it was a joke.