My brother might be leaving Islam and I’m heartbroken

Salaam everyone, I need some advice about my older brother. For a while, it seemed like he wasn’t really practicing, but I figured he was just on his own path and that’s okay. But lately, things have gotten worse. Last month, he started questioning a lot about Islam, and I told myself that’s normal. Then I saw he shared a video online saying something like “what’s the point of dating if it’s not to pursue Jesus.” When I asked him about it, he said it was an accident, but we ended up arguing. He never removed the post, and we didn’t talk for days. I’ve also found pork products in his room a few times. A while ago, he mentioned that his ex-wife used to try to convince him to become Christian. The friends he has at school aren’t a good influence-most of them are Christian or atheist, and he barely has any Muslim friends. I think this has affected him a lot. Today, we had a huge fight. He challenged me, saying if I’m such a good Muslim, why don’t I wear a burqa? He kept asking why I don’t fully follow God’s words. I kept asking him, “Are you Christian or atheist?” but he wouldn’t give me a straight answer. He just said, “Whatever makes you happy” and then walked off, adding, “Because it’s not my religion.” I was so angry. Then he wanted to debate privately, but he still wouldn’t answer my question, just saying it’s obvious. After that, he threatened me not to tell anyone about our fight or that he might not be Muslim anymore. He said he’ll explain himself when the time is right. Part of me thinks he’s just saying these things to upset me. But I don’t know. I said some harsh things too, and now I feel lost. I can’t imagine my own brother rejecting Allah. I remember when we lived in a Muslim country, he used to run to the mosque to pray with his friends, even though our family wasn’t strict. I grew up in different places-a strict Muslim country, a more relaxed one, and the West-so I try to be open-minded. But my brother is only 16 and has mostly lived in the West. I feel so betrayed. We’re really close; he’s always been there for me, and now it feels like I’m losing him. I don’t know what to do.