What About the Plans We Made?

I keep having this thought, its a lyric from Billie Eilish song:

I'll be in denial for a little while longer—what about the plans we made?

My therapist says I need to write a goodbye letter to you and read it aloud.

It's the only way to start healing, so that I stop feeling like I walk around with a broken heart in a path full of thorns.

The feeling is too raw to get into it, but the thing is I'm also willing to wait until eternity—but that's not living.

I need to say goodbye to what could have been, because what we had will always be with me forever.

I don't know where to even start with the letter.