|It is time to recognize the fact that you have one manager in name, and another manager in fact. For whatever reason, your manager has abdicated his managerial responsibilities over you, and they have been assumed by another.|
The only possibility of resolving this matter is to meet with your manager and discuss what is going on here. On the one hand, perhaps he is unable to give you the time you need because he is immersed in other critical projects at this time. On the other hand, he may just be incompetent. Or, perhaps it is a combination of the two. Either way, it is not a good sign that all of this has transpired without any communication to you.
Let your manager know how you feel about current developments, and add that you can be more effective and productive by using and building upon the strengths and skills required in your original position under his leadership. His action and reaction will soon tell all. If he has permanently walked away from managing you, then you are actually in an entirely new job. The question then becomes whether you want to manage it or walk away.