camo (as in, camouflage)?
Over time I am worn and worn away like anything else
Camo is certainly worn, as clothing; not sure about being worn away.
A close cousin of mine treks through desert though I prefer the forest
Camel (close in spelling/pronunciation), a desert dweller. Camo is commonly seen with the dark green/forest color scheme, though 'desert' and 'urban' camo schemes are also used.
Double the third and remove the first and I become a little bit explosive
CAMO -> AMMO.
Remove the last and you may see yourself in me someday
CAMO -> CAM. I can see myself when i look at recordings from my webcam.