How to tell parents you're not ever coming home?

Don't put it as "not ever." Say "I found a great situation that's good for me, and I'm going to do that. I'll keep in touch with you guys." If they ask when you are going to come home, just say you don't know; you're going to pursue these great opportunities and see how they go. If you are an adult (?) then moving out was going to happen sooner or later. And if a sibling or trusted friend can go over and get your stuff for you, have them do so. But if a bag of souvenirs is the price of your freedom, it could be worse. Be prepared for them to be unreasonable no matter what you do, and just get it over with.

You are in control now. Disclose only as much information to them as you see fit. You're an adult who doesn't need to justify anything to anyone, not even your own parents. On preview, qxntpqbbbqxl's explanation sounds like the best hope for getting your stuff back.

So...presumably, you need to find yourself a storage unit for your stuff, and go home at least once more to get it. You can't say you're never coming home but keep all my stuff, thanks.

Yeah, just to second everyone else: you can't have it both ways. Either you do live there, in which case your stuff is in your room, or you do not live there, in which case you're using someone else's house as a storage unit. It doesn't matter if it's your parents, or the codependancy or whatever: it's an either/or situation.... you live there, or you (and your stuff) live somewhere else.

Consider also the possibility that the things you've left at the house aren't necessarily so important.

I'm confused about what the actual situation here is. So you're currently working away from home, and you've made the decision the decision not to return home at the end of the gig? Or maybe you've been offered a permanent contract? Bottom line, regardless of what your parents are like, is that unless you're sixteen years old, this is a normal thing. It shouldn't need to be something you have to brace yourself for. Most people eventually grow up and move away from their parents' house. Yes, it sounds like your parents might freak. It might be hard for you to hear. You need to stay strong and stick to your guns. Not physically being there will probably make it easier. The only thing you can really control is saving your stuff. You mention a brother - can you have him grab that one important bag before you fill your parents in? In terms of your last paragraph, I'm a strong proponent of not filling parents in overmuch about the day to day when you first strike out on your own. Because, yes, people have highs and lows and good days and setbacks, and if you tell your parents every little thing, they will find excuses to shut you down or "come to the rescue". I don't think you should explicitly lie, but there's nothing wrong with letting them have an understanding of the situation that is a little bit more optimistic or that would make life easier for everyone concerned.

This reads as if you intend to never come home again, but that there are things that belong to you that you want to keep in your old room indefinitely. Can you clarify? Because I think if you really do want to be able to move to a situation with no in-person contact (or perhaps no-contact entirely), you first need to make some sort of clear plan as to how you're going to take responsibility for your own possessions.

What emjaybee said. Don't tell them. Just keep coming up with reasons why it won't be now, or next month, or the next 3 months.

"Hey, Mom. My friend X is going to come by this weekend to pick up a box of stuff from my room. Yeah, I'm sorry for the inconvenience, but she needs it for reasons." Then you can tell them everything or nothing at all about your future plans.