Sadly a reason why her husband cheated on her, he wanted besides a mother to his children - a lover playmate and a regal Empress, which to him his favorite long time mistress and later morganatic wife Ekaterina Mikhailovna had.
Maria Alexandrovna had poor health all her life which worsen with age and to the Russian Court, they saw her much how the they would see her great-niece Alexandra Fydorovna in the 20th century - a German, from a poor court (same court Darmstadt), weak & mental heath, bad taste in fashion, way to shy, heartless saying she didn't care for Russia and it people etc...(however AF would have a happy marriage with a faithful husband).
As being protective of her children, she was especially protective of her eldest son and heir Tsarevich Nikolai Alexandrovich and after his death and the memory of losing her eldest daughter and child Alexandra many years before- haunted her for the rest of her life and she cling to her three youngest children (Maria, Sergey and Paul) and spend long periods away from Russia in her birth county Hesse with those children.