Distance Tracker Help

[Mr.Pilot]

Alright I'm completely stumped and I'm hoping to see if anyone here has an idea,

I was making this SWEP, for practice, and to go a little over my comfort zone with programming, but I got stuck.
I was trying to make this thing like when you left click (SWEP:PrimaryAttack()) and it is a player then it is bound to you.
When it is bound to you it means if that player walks, lets just say 2000 units away from you they would explode. Sort of like a wireless chain that connects you to that player.

If you guys could help me that would be fantastic. I know it's annoying to help people without anything back, but for you good guys out there, I'll give you a big thanks.

EDIT:

Alright, read that clusterofatext if you want to understand what I'm doing, but this is what I really need now. I have

if trace.Entity:IsPlayer() then
     return
end

And so instead of "return" I want it to get the player and remember it for another function. How would I do that?