Complex sentence: George is very mature for her young years and Cal often finds himself fascinated and somewhat attracted to her; a thought that scares him, although George has so far assured Cal that their relationship is that of a brother and sister.
Split into simpler sentences: George is very mature for her young years and Cal often finds himself fascinated and somewhat attracted to her; a thought that scares him. Although George has so far assured Cal that their relationship is that of a brother and sister.