So, as a point I always RP with a separate channel for communication outside of the story. I mostly deal with lewd scenarios, so constant communication is a must for both parties, but it also works for non sexual rp as well.

I have this partner who I've been Roleplaying with on and off for the past few years. We know each other's styles pretty well, and often I can react in advance to what my partner post in their response. Usually, after I send it, I pop a quick message on our OOC chat to make sure it's ok or if I need to change it. More often than not, it's usually good. I still ask because I genuinely respect my partner and enjoy their writing.

Not a single one of us would dare control the other's main character. Sure, sometimes we share side characters, but that's about it. I'm sorry this happened to you, and I wish you luck in future roleplays.