A: Your situation is complicated, but it sounds like you are beginning to feel uncomfortable with the co-sleeping arrangement, which I think you should pay attention to. Two principles apply to your situation. First, co-sleeping does not have negative psychological outcomes when it fits within the cultural preferences of the family. In communities where co-sleeping is widely practiced (as it is in much of the world) or where parents make a conscious choice to co-sleep, studies show there are no negative psychological effects on kids compared those who sleep independently. However, when it does not fit into cultural norms or when parents have not been successful in getting a child to sleep independently, studies show there are negative effects. (This is separate from the serious physical risks of co-sleeping with young children, such as falling out of bed or being suffocated.) Second, parenting that serves the emotional needs of the parent more than the child often leads to more problems.
Our society, for better or worse, emphasizes childhood as a process of growing independence, which includes emotional independence. Perhaps it is time to sit down with your son and talk about when -- not whether -- it would be appropriate to transition to his own bed. It's also crucial to make sure that you have other people to lean on emotionally other than your son, if you do not already have those resources. As he gets closer to adolescence, he may rebel against his role as your support, or he may do the opposite -- he may take that responsibility so seriously that he will have trouble becoming independent.
Because of the complexity of your situation, I would strongly encourage you to consult a licensed therapist or qualified professional who has expertise in trauma, bereavement, and family issues.