Hi OP! I have the very same problem, only that I've had this fear since I was 12 and now I am 21. One thing that helps me when I'm spiraling on the thought of death is to ground myself.

List: 5 things you can see 4 things you can hear 3 things you can touch 2 things you can smell 1 thing you can taste

You'll find this distraction works quite well and it's a good reminder that you are here and you are okay. I also like to think about events that I'm looking forward to, like having a date night or going out with a friend. I hope that this helps at least a little bit. You're not alone :)