You have got hidden fear of your habit of masturbation
,You do not worry for your this habit.One never gets weakness with this habit so remove fear from your mind,you develop your self confidence and decide that I have to speak on the stage in front of crowd,I am sure your stammering
will go away !
You are suffering from inferiority complex
precipitated with false fear of your habit.
You can consult psychologist
for counseling and speech therapy