I completely understand this, and underwent something similar lately. Some people here had great ideas about why, especially that there is a "therapy bubble" inside which the relationship feels so real, but when the T leaves, it is revealed or we are reminded of what we do always know but kind of put aside- that it is actually fundamentally not a "real" relationship in our real lives. It hurts. I don't want the feelings either- the sense of loss is so hard to understand. Hopefully we will figure it out, and end up somehow growing from it.