I think, for me at least, attachment brings some pain with it, some longing. The wish to be more a part of their life than the boundaries of the T relationship allow. Pain if I get any sense of rejection from them, like tightening boundaries. If they cancel a session at the last minute (or even the night before), I might end up crying or at least feeling sad or let down.

Liking is more, "I want to spend time with them," but without the need. Feeling they're helping you, but not feeling like it could be the end of the world if, for some reason, you had to stop seeing them or they tightened boundaries.