Seen similar scenario where girl is controloing and basicaly a first serious GF for a guy. Sometimes she was dominating sometimes him but in the end they love keeped them together and they did benefit from each other. 4 years is not a joke there must be some magic behind that thats for sure, maybe its better for your bro to be together with her rather than single. In mean time be a man and stand up for yourself dont let her or any other stupid girl roll over you by any means.
Doubt kills more dreams than failure ever will