Assalamu alaikum - I think I love my closest friend

Assalamu alaikum, I don't quite know how to start, so I'll be straightforward. I'm seventeen, a Muslim man, and I've tried to live by my deen. I pray, I try to be consistent, and my faith matters a lot to me. Still, I'm struggling with something I can't talk about openly. I have a companion, my dearest friend. We've known each other for many years and grew up together. He's the person I trust most. When something good happens, he's the first I want to tell. When I'm upset, he's the one who comforts me. We used to pray together, study together, and go to the masjid. He felt like a safe place. Lately he has left Islam. This hurts more than I can explain. I make dua for him every day and sometimes I cry. I'm afraid for his akhirah. But there's another issue too. I think I'm in love with him in a way that feels more than brotherly. I know we're commanded to love for Allah's sake and that good friendship is valuable. But this feels different. When he's sad, it breaks me. If he turns away, I can't focus. Seeing him with others makes me jealous and ashamed. When he talks about leaving the country, I panic. I find myself thinking about him constantly, worrying if he's okay, replaying our conversations, missing him even after seeing him that same day. I've never pursued a relationship that would be haram. I've never crossed boundaries physically. Yet my heart is attached in a way that scares me. I try to tell myself it's just friendship, that he is my brother and this is normal. But if it were normal, why does it hurt so much? Why does it feel like a sin? Why do I feel guilty just for having these thoughts? Since he left Islam, the feelings have become heavier. I'm scared of losing him and becoming distant. I worry Allah is testing me and I'm failing. Sometimes I wonder if these feelings are the test. Sometimes I fear they are sinful. Sometimes I fear I'm broken inside. I've tried creating distance, but it's like cutting away a part of myself. When I do, I only feel emptiness. I still pray and make dua, asking Allah to heal my heart, to remove what is wrong, and to guide us both. But I'm tired. It feels like daily inner battle. I love Allah and don't want to displease Him. I also love my friend and can't figure out how to divide those loves. So I'm asking sincerely: is this attachment sinful? Can one love too deeply even without acting on it? How do I let go without becoming cold? How do I protect my iman when the person I love most no longer believes? Please don't judge me - I'm trying and I only want to do what's right. (Please excuse my English, this was translated.) JazakAllahu khair.