In my opinion its time to replace that string. I change strings on my bows about every 2yrs or so, sooner if I shoot and hunt alot. Even if you have not shot the bow alot the elements still have an effect on the material of the string(thats my thinking
). I try to wax string after shooting this will protect it. Keeps the fibers of the string together plus lubricates the binding material, from time to time I will also wax serving as neeeded.