It must be hard for you. You sound really gutted in your post, but it is an age thing to a certain extent..

My DD is a month older than your DS, and she is starting to want to play on her own without her brother. She pushes him around, bullies him, yells at him and shuts him out of their room.

I have a smaller age gap (21mths) and DD is used to playing with her brother,but she is starting to want some time to herself. She wants to do things her brother can't do, and it does cause problems.. I am just encouraging some play time together, and some apart,but I don't know how to fix it either.