Most Helpful Guy
Maybe try getting a attorney to write up a letter telling him you want your stuff back or your going to take legal action against him.. Yes any guy who keeps a girls things for 4 months is not the type of guy you want be with... That's what happens when you fall in love when your only 16 not that good to exchange stuff with each other at that age way too young i can see at least age 18 but that should be the limit.. Really there may not be much that you can do about getting your stuff back but the threat with legal action might put a scare into him so he will send your stuff to you really hard to say..
Most Helpful Girl
Unless there are assets, or some kind of heirloom you want back, then sadly, forget it. Sometimes you have to consider the price of a relationship, and it is lesson learned - take your stuff before the break up next time.
You just said it yourself, he's immature and emotionally abusive. You think he's going to turn in to Mr. Great Guy after a break up now and give you your things back? Hell no. He's going to make you miserable and keep contacting him begging him for it because that's his only form of control over you now. Unreasonable exes do this to "get back" at their exes for ending it with them. I had a guy nag at me for two years to give him back a message in a bottle curios that was worth maybe $20 he could have picked up again where he got it from, but oh no, he had to piss around and harass me for it until I changed all my contact information to make him stop it.
It's not worth it. It's been four months already. Consider that your parting gift to him and let him sit there and stare at it and get himself all in a twist that he has no choice but to keep it or make an effort to give or throw it away.
Sometimes you have to cut your losses, and I think this is one of those times. Get new stuff and detox this person out of your life. He knows he's being stupid. He just thinks he's got the best of you, but when you move on he'll have no more power over that and realize all his immaturity to get to you was wasted effort.