I am not a stepmom but we have a blended family so I have some experience with roles and expectations in that regard. First, is your husband the main caregiver parent of the boy, or are you? I would try to minimize your involvement rather than assert yourself here. Due to his disability and age the stepson may not be able to manage his emotional responses or relations with a woman, especially if he perceives you as not being his "real mother." This is the time, it seems to me, for your husband to take charge with love and acceptance and guidance and discipline; you can and maybe should leave it to the men to work this thing out. I would see your role as "supporting" at this point: asking and listening about the son's activities, doing things behind the scenes like making a favorite meal or bringing forgotten items to school, and generally being a silent support to both your husband and the son.
I found that with teens they will match your strength with a show of greater strength, and if the stepson cannot realize this tendency as a phase or manage his responses and self-image, then you could be the object upon which he discharges his frustrations and against whom he gains personal power.
Most of all I would try to stop fighting with your husband about it. You are both demonstrating to the child that he is more powerful than both of you together if he can make such great discord with so little effort. What everyone needs is progress and you don't have to be the leader - probably cannot be, due to the circumstance - but you can enable the men to make progress by staying out of their relationship. I would say as much to your husband, with love and hope that a change for the better will follow. Then privately work on your anger and resentment so that you don't bring that to your relationships.
You should also consider privately what future for the young man is good for him and acceptable to you so that when this time passes you can be calm and rational with your husband about constructive options for the family when the boy becomes an adult.
Last edited by pumabearclan; 06-05-2014 at 10:22 AM.