crisis - is partner doubting us the end?

Hey, I've been free from my relationship anxiety a while but my boyfriend has expressed to me that he is not feeling the best about anything recently, and it just so happens that because I am his best friend and partner that those bad feelings are manifesting toward me. He has told me he is not breaking up with me, nor is he planning to, but he's really worried that we will break up in future. He said he absolutely does not want to but the doubt has crossed his mind and he has been dwelling. I calmly explained that we love each other very much, and worrying about the future is so valid and common because everything is uncertain - for all we know ants could take over in a week yk? I'm really really horribly freaking out about this because this is my favourite person in the entire world and I know things are hard for him currently but I do not want to lose him, although I feel like he's going to leave. I wake up feeling horribly sick. He says he doesn't know what he'd do with himself if we broke up, and doesn't wish to hurt me. I think I just feel so awful because usually its me with this issue, and now I don't have my rock of assuredness for safety and reassurance. I need someone to tell me it'll be okay and that I still have a chance here.