I would take some of the super glue that is thin and fill the gap. Let it run into it and seep in till it runs out on all sides. Let it sit for several hours. Then take a fine emery board ( you may have to make one) and sand the excess hardened glue off.
It appears that the wood may not have a finish on it. If this is true, it will eventually crack again, unless you seal it. After the above procedure, I would put straight linseed oil on it and rub it in good and let it sit for a day or so. This wont change the look very much, if any, and will preserve the handle wood better. Lin