I don't think being 'smart' (presumably you mean intelligent), beautiful and romantic excuses affairs, particularly when they produce offspring of dubious paternity which the husband is then obliged to treat as his own (poor Ferdinand!).
In any case, I'm not mad about Marie's looks. She was distinctly chinless (note that no photograph shows her in profile!).
As to whether a marriage to George would have worked, there are indeed too many variables to predict, but I fear it would have turned out rather like Charles and Diana. George was nearly 10 years older than Marie, and distinctly middle-aged in temperament, at a time when Marie was still a teenager. At that point in her life, a steady mature man might well have seemed an ideal marriage partner, but I think she would have got bored with George and then the affairs would have started.
Ann