The first bout of abandonment one knows about in the play is Amanda's husband leaving the family way back and crippling apparently her common sense, the security of the family, and the self-esteem of Laura from what one can gather.
Second, it almost seems as if both Tom and Laura have an issue with abandoning goals, plans, opportunities. Laura left her typing courses due to what one would call social anxiety, and Tom basically has abandoned his responsibilities at work and as a family member in search of a dream that he cannot even concretize.
In the end, Tom does end up leaving the family, and the entrapment he feels from his mother who is overbearing and still lives in her own past world. Leaving the house means abandoning Laura as well. In the same Act, Jim, Laura's life-long fantasy reveals that he is engaged to marry, thus there is another abandonment that Laura feels inside, this time from one of her fantasies. When Tom leaves in the end, Laura blows out a candle as if the uncertainty of each character will not be cleared nor enlightened by any other cues.