INFJ or INFP? a closer look
Go to the drop down menu at the top and click on "Interview about feeling differences."
You are not alone in the way you are. It is just your INFJness coming out.
I am INFP but borderline INFJ.
It sounds like you respond to the emotions of others and do so very well. That is a strength. But when you are alone, you don't know what to feel.
To get more in touch with Fi, you just have to look back at moments in your life, no matter how mundane or life changing they were, and think about how YOU felt about them.
I don't know how to explain it well, but you have to put yourself in the place of others. You gave an example of your father's infidelity and that you won't do that because it hurt your mother deeply. Go back. Imagine you are your mother. Feel what she felt. Imagine it happened to you.
Then watch a movie... something that takes you on an emotional roller coaster (Eternal Sunshine of the Spotless Mind perhaps). Imagine yourself as both main characters, feel what they feel. Don't "respond", but "BE" them. Don't try to mimic their emotions, feel whatever is natural for you if you were put in those situations.
That being said, I don't think Fi can be taught and learned, but it can be practiced.