Complex sentence: Gehrig's mother, who still hasn't accepted the fact that her son will not be an engineer, does not take the news of his pending marriage well; but Lou finally stands up to her and marries Eleanor.
Split into simpler sentences: Gehrig's mother, who still hasn't accepted the fact that her son will not be an engineer, does not take the news of his pending marriage well. But Lou finally stands up to her and marries Eleanor.