Here is my situation: I am a Ph.D. student in theoretical CS. Since the start of my Ph.D. I have been sending my advisor the descriptions of my results verbally, he would usually ask me a bunch of clarification questions and I would answer back. Usually after some repetition of the questions-answers process (which usually lasts for about a month), he would declare that my result is correct. At that point, I would always ask him if he could write it up and he would agree.
Lately, it seems he is producing more papers so he stopped collaborating with me. He said that the time it takes him to formalize my results is almost equal to the time it takes him to write up his own papers.
My results are usually about the same level (they're shown usually in A-rated conferences) as my advisor's own.
What can I do about it?