Can't stop thinking

I just can't let go of the thought that one day things will all over and different, and that I'll lose people. I'm kinda scared of the future as I'm not sure what I'm gonna do and I just can't stop thinking about how things will all be different.

Like this sounds pathetic but I leave school next year and this is really getting me down. Like how everyone's gonna die and things are gonna be different and I don't fit in. I don't enjoy school but at least it's a constant.

I also miss how things used to be, and the person I used to be. Any advice?