"I don't know how to thank you enough for the role that you play in my life"

Overheard gf to her bf. While I am sure that her intention is good with this compliment, it does shine a light on the underlying machinery:

You are not her priority, she is completely self centered. You are a "thing", that plays a "role" in her life. Your role is to make her life better.

She is thankful while you are doing it. What will happen when she "thinks" that you are no longer adding value to her life?