Are we called to unconditionally forgive a bad parent (getting old) when there is no the slightest sign for repentance or ask for forgiveness?
To what extent the fourth commandment applies to an abusive narcissistic parent?
I am afraid my soul is in the state of sin for harboring such feelings of resentment towards my mother. I am an only child and feel like during my entire life, I have been just a scapegoat for her emotional turmoil and pathetic immaturity. She is infantile, like an wounded child who never grew up. Father, or course, was absolutely absent from my life (all her doing - she is a Feminist).
Yes, we're obliged to forgive unconditionally, because there were never any conditions given by Our Lord, or Tradition, as to when not to forgive. And we're obliged to provide for our parents when they need help, as much as our situation allows.
I have the same trial. I try to do these things to overcome my resentment:
Remember Blessed Margaret of Castello.
Remember that of those to whom much is given, much will be expected, and of those to whom less was given, less will be expected. This helps me if I'm tempted to envy people from good families.
Remember the reward in the next life that's promised to those who keep the Commandments.
Remember that you, as long as you're in a state of grace, are Heavenbound, and your mother doesn't seem to be. Try to pity her, if you can't forgive her yet. Imagine her in hell, if you have to, to arouse pity.
Take care of yourself and see to your needs without looking back on your childhood, which is in the past where it belongs.
Remember that when you're angry or resentful, it's a kind of insult to God, Who gave you that mother for your sanctification. Try to figure out what He might have had in mind for you in that regard. How might He expect you to sanctify yourself with such a mother?
Focus on the present as much as possible, not the past nor the future.
Take your feelings into your prayer life and try not to complain to anyone except maybe a close friend or two. It can be a hard habit to break, but it really helps everyone.
Keep thanking God for showing you all these things about your mother.
It goes without saying, I hope, that your prayer and sacramental life should come before any advice. I'm just sharing other little practices that have helped me.