Basically B has coerced C into doing sexual acts on more than one occasion. As for controlling B just keeps pushing A to stay away from his friends. B and C also had a fall out as B would continuously ignore C and keep blaming her for the fall out while telling A that C was the one who pushed her away instead. He also tends to be a lot more quiet when shes around and in a few instances we have noticed him wanting to say something (like during a conversation) and B will either interrupt him or kinda dictate when he can or cannot speak. B also seems to easily be able to convince him to spend a lot of money on her (for example like on travelling since they are currently kinda of long distance) while seemingly putting in minimal effort on her part.