As an aunt who adopted her neices and had her nephew and a former foster kid and such I have very big concerns about this. I think that living with the same person since you were four the person who is your whole world your emotional support your secure base and being taken from that is very big. I think that if this is what you feel is in his best interest over all in the long run you must take it very very very very very slow. Visits that gradully increase over time. No matter what you feel about your sister it doesnt matter what matters is how your son feels about her. Ripping him out to soon will leave a lifelong scar. I can tell you about those if you want. Like fearing attachement being afraid of any type of seperation...not trusting people. I cant stress enough it has to be slowly. Why not share custody for now? Why not do it like that? This is a seven year old baby. I know that he is yours and so on but he didnt do this you did and neither did your sister. Its done and I am glad your better but now its time to really focus on whats best for your son.
Not saying you should not have him back if thats whats best for him but what I am saying is that it needs to always be focusing on your son not what you dont like about your sister or what your sister doesnt like about you.
Also maybe having some empathy for your sister also. She has taken care of this child for three years. She has loved him and treated him as her own. She is attached to him which is good, for your son. I can speak from my heart and say that I love my neices and my nephew as if I had given birth to them. Your sister is probably afraid now. WHy shoudlnt she be? She loves this child. You have to have empathy for every one in this this is your mess you made (not to be mean but truth ((HUGS))) so slow down take a deep breath. Look at things from you babies point of view. Talk to alot of child attachment therapists. Dont wait until heis moved to find a therapist. Let him start now. You have to do this so that the damage is minimal. You have to focus on your son. Right now your sister is his comfort his secure base no matter how much you hurt be thankful he has that. Alot of kid get put in foster care and they really get screwed up as they dont have that secure attachement. Be grateful and thoughtful to your sister. No reason to rush this. Really examine and think if this is the best for your son also. Ok ((HUGS)) hey pm if you want I can give you my email and I can help. ((HUGS))