Evidently the nurturing role you have learned in dealing with your father must be noted when you meet these other people who have only one parent. I didn't quite understand what you were saying about your girlfriend, but I assume it was that she is thinking of you as like her dead father.

Do you have access to a ACOA group in real life? Maybe you can talk to some of them about it.

I would talk to your girlfriend some more if I were you. Some women are attracted to father figures. That can be okay, depending on what they want from a father. Most women do want some nurture, but is your girlfriend also able to stand on her own two feet?

You might also consider some therapy to try to work on these issues, given that your father will be requiring even more role reversal if he lives long enough and becomes less capable.