This honestly doesn't seem to be about the music. You seem fixated on this, like by playing the right piece, you are going to get something FROM your therapist out of it. Maybe that's really what is going on here so maybe you just need to explore what you are thinking you'll get from this (which is probably why your therapist questioned you about it; I'm guessing he thinks you don't even realize what you are trying to get out of it and also feels this isn't really about the music).

I'm a musician. If I was going to share a piece with my therapist, I would know exactly why and exactly what piece because it would be about the music and its connection to something very specific in me/my life. I'm not getting that sense from you. I'm getting a "I want to place this music to gain some cosmic connection to my therapist" vibe which I'm afraid you probably won't get and then this will become this several weeks long thing where you analyze why your therapist isn't understanding you or connecting to you or something like that.

It all seems, as someone else mentioned, very teenager-like. Very fantasy-like. Rather than very truly specifically purposeful.