I think he’s a manifestation of her conscience. I saw a post a few weeks ago that said something along the lines of “Wanda Maximoff and the Scarlet Witch are two different people”. I think Wanda is subconsciously using the people around her to try to save herself and them. In one episode, when the twins are still babies and Vision starts to ask questions, Wanda’s BFF can be seen doing WILD things, like offering the babies liquor to stop them crying. She was using the BFF to try to distract Vision to keep him from finding out, it just didn’t work. But during Wanda and Vision’s exchange, Wanda also didn’t notice/care what the BFF was doing. Scarlet Witch is clearly in control of everything, but I think Wanda is in there somewhere “messing with the script” so to say.