This one can be tricky. We are usually not very good judges of our own progress, because we have lots of ideas about what progress “should be” that might actually expectations we pick up from others, society, etc.
I think one of the ways you know you are changing is when your relationship with yourself and your struggles starts to be more productive, compassionate, kind, and forgiving. You feel you have more choice, more agency in your life, over yourself and your behaviour. You really feel “like yourself”, or at least you know what that is.
It’s not that you will come out of therapy being completely “perfect” and “healed”, but that you come out knowing something important about yourself and others that you can access and apply in your everyday life.