Looks like you've tied the furling line directly to the ring on the tail. That means, as the tail swings back-and-forth in normal operation, and the furling line is wiggled by the wind, there is constant wear on the line - in the perfectly worst spot (the center of the bight). Next time you really need it, expect it to break again.
I'd line the rope bight with a "rope thimble" - a metal liner for a loop. That way any wear would be metal-on-metal and the rope would be protected from abrasion.
An alternative would be to tie the furling line to a ring through the welded loop, or the loop itself, with an anchor hitch. (I'd probably follow that by parking the end of the line with a couple half-hitches back around the running line, to keep it from flapping.) That gives it a grip on the loop and keeps it from sliding around and taking wear (except maybe just when you actually pull it in, in the to-the-welded-loop case).
My wife's boat, in a marina on the Alameda Estuary, has been moored to a ring-through-an-eye with this knot, for years, taking several hearty yanks per minute thanks to Pacific-ocean-derived wave action. There was no sign of wear (on THAT end) when I finally got around to periodic replacement of the mooring line. Took a couple minutes to get it untied, though. Very sturdy knot.
