Complex sentence: Leslie disapproves of Bruce's vigilantism, and feels partly responsible for his transformation into Batman, fearing that somehow she failed him as a role model, although he has admitted to feeling guilty for being unable to live up to her pacifist example.
Split into simpler sentences: Leslie disapproves of Bruce's vigilantism, and feels partly responsible for his transformation into Batman, fearing that somehow she failed him as a role model. Bruce has, though, admitted to feeling guilty for being unable to live up to her pacifist example.