Struggling to Stay Firm in Faith After My Father's Passing

Assalamu Alaikum. I hope you are all well. I’m sorry if this feels like complaining, but I need sincere advice and I hope what I say isn’t sinful. I’m scared of losing my iman. My father passed away recently, completely unexpected, and I didn’t get a chance to say a proper goodbye or make things right. It’s been very hard for everyone. I’ve had to take on a lot more responsibilities. My mother is very low, my younger brother is relying on me, and my grandmother is devastated. Strange as it sounds, sometimes I feel like I had the least to lose and that hurts - I don’t really know how to explain it. The first few weeks were the worst and the pain has eased a bit, but I still struggle. I tell myself death was better for him and remind myself “Inna lillahi wa inna ilayhi rajiʿun,” but often it feels like something I say to comfort myself rather than something I fully believe from the heart. At first I was steady; I kept repeating those words and felt sincere. Now I feel lost. My salah lacks khushu‘ and doubts keep creeping in about my faith and about the Prophet ﷺ. The waswas has been overwhelming lately. I’ve been asking Allah to renew my faith, but my heart doesn’t feel sincere. I feel distant from Allah. I tried reading the Seerah of the Prophet ﷺ to strengthen myself, but it hasn’t had the effect it used to. If I’d read this a few years ago, I would have been inspired and moved, but now the whispers are there too. At my father’s janazah I stayed calm to support my mother. I held her hand and tried to comfort her, saying things like the next time we meet him he’ll be free of pain and we’ll be young without worries. He died a shaheed, so I mentioned that too. There were female relatives nearby, and later I worried my intentions weren’t pure - maybe I wanted to appear composed or strong rather than truly comforting my mother. I know intention matters a lot in Islam. How do I sincerely repent for that? Sorry for venting. I’m worried that complaining is sinful. I’ve said worse things in my head and out loud, and I don’t know how to take them back. Please make dua for me and give me practical tips on how to regain sincerity, increase khushu‘ in prayer, and deal with waswas after losing a loved one. JazakAllahu khairan.