Mary Tyrone's obsession with her past ruined her present.Commentplz answer in detail

In Eugene O'Neill's Long Day's Journey into
Night, Mary Tyrone cannot find happiness in the present because she is
emotionally stuck in the past. She constantly thinks about her girlhood, before she met
James Tyrone, and wonders whether her life would have turned out differently had she
never met him. Her life was simpler then. She lived in the convent and was happy there.
She was also becoming a skilled pianist. Now, with an alcoholic husband who has not
provided her with the home-life she expected, two alcoholic sons who both turned out to
be disappointments, as well as her own morphine addiction, it is easy to see that she
will never be able to return to those past, idyllic days.