For that fight, you should have aid from a few other npcs. One of those npcs is a healer type, the other is a tank type. Wilfred is a melee dps type i believe.

The key to this fight is to keep both wilfred and the healer alive. The tank type can take the hits, but the other two cannot. I would advise against outright healing as an archer though, since you have less mp and cure isn't a very powerful heal unless you have the MND and magic attack gear for it.

Leave the healing to the npc. When you notice the adds, quickly burst the ones down attacking wilfred or running towards the healer. Feel free to use shadowbind to stall enemies from reaching them if you can, and interrupts to disrupt enemy spellcasters and aoe. It's a tough fight (I know I retried at least 4 times on it), but employ a combination of damage and cc abilities. If you can't kill them fast enough, then try to draw aggro. Kite the enemies around and the npcs will peel them off you eventually. The trick is to limit the number of attackers on the npcs. They have high hp, low armor, and can heal/dps a large amount of damage.

You do get a substantial buff to stats after failing it, but if it still doesn't work, consider upgrading your equipment (notably your bow).