[quote]If you find a gun and you fall in love with it. Will you eventually have to drop it of because it will be completely week once you unlock new weapons. Or will all the guns be balanced?[/quote] Yes eventually it wil be weak. For PVE. HOWEVER. Competitive multiplayer in the crucible. U can use whatever and its balanced .

You can upgrade guns as well so you could hold on to it if you want

You can dismantle weapons you no longer have a use for. You'll get a little bit of glimmer out of it, as well as some materials if the weapon is a rarity of uncommon or higher. Balancing of weapon damage is present in the Crucible (Destiny's PvP area/game modes) but in PvE (player versus the AI enemies) weapons will have varying damage outputs.