I don’t think it’s a matter of whether he’s jealous or afraid you’ll be taken away or whatever. I think he’s just being a dick. Sometimes teenagers discover dickishness gives them a rush of power (because everyone just kind of shuts up when they crush them with their overt assholery). But to be honest, it doesn’t matter why.

Your brother is being extremely rude. This is an issue of boundaries and standing up for yourself.

If he butts in when he’s not even part of the conversation, perhaps try responding like that’s the most unexpected and rude thing ever: “Excuse me? We’re having a conversation here,” or, “If you would let me finish please?” If you’re talking to him and he’s rude, dismissive or critical, just dismiss it. “Right. Thank you for your opinion. Do you want me to just shut up, then?” Another good one if someone is being rude is to just call it: “How rude are you!” or “Don’t be rude. I was talking to mum.”

I know it’s easier to just shrink and stop talking about the things that are important to you because your overbearing brother will have some negative thing to say about it. The problem with that is that you will shrink as he expands, unfairly, at your expense. I think it will hurt your confidence and, in the long term, your social skills if you let him shut you down like that.

It sure sucks to have to deal with someone so critical, dismissive and interrupting in your own home. But if you shrink to accommodate him, the next asshole in your life will have that much easier a time walking all over you. You don’t have to fight, but you have to have boundaries.

Have you talked to your mother (or other family members) about how you feel? Can you get them on your side? Have you tried a calm conversation with him about this pattern of him dismissing your interests and likes? Maybe he doesn’t realise what he’s doing. It wouldn’t be good for him to grow up an asshole, either, so really you’re doing everyone a favour by not rolling over.

It’s tough though. Good luck/work hard.