Call your son and explain what you've learned about parentification. Tell him that you now realize that you were parentified as a child and did the same to him. Ask for his forgiveness. Most importantly, don't fall back into that safe and familiar role reversal ever again. From now on, be a mother to him and provide the unconditional love and support that every child craves from a parent.
Over twenty years ago, my mother and I were listening to a radio call-in show when the host, a psychologist, took a call about parentification. It sounded all-too-familiar to my mom, and she immediately turned to me and apologized for using me as her marriage therapist when I was a teen. While I was impressed that she recognized what she had done and expressed remorse, her behavior never changed.
She continued to use me as her therapist (telling me about the problems with her boyfriends since my dad was now dead). With a husband and kids of my own, I had no other choice but to distance myself from her. I needed to focus on my family and not be overwhelmed with her never-ending drama.
In telling you this, I'm making the point that an apology means very little unless it's backed up by actions. Changing how you see your role as a parent will be extremely difficult because it's deeply ingrained. Albert Einstein famously said: “No problem can be solved from the same level of consciousness that created it.” Taking parenting classes. talking with a therapist, and building a support system of friends would be extremely beneficial to helping you see mothering in a whole new light.
Your ultimate goal is to become a “transitional character” and put an end to this dysfunction that has been passed from one generation to the next. I don't know if you can repair the relationship with your adult son, but you can certainly avoid repeating the same mistake with your younger kids. You may want to read my article entitled: “How to End Family Dysfunction by Being a Transitional Character.”