Your brother in law has no right to appoint himself your caretaker because you have certain problems. What he has done was humiliate you, insult the dealership, and made it nearby impossible to do business with them again.
And your husband? where is he in all this? Does he regularly let his wife get dragged around by his relatives?
And hon, (huggs here) you do not have to go along with this, or is there something here I don't know? I know when we people who have chronic mood porblems have our judgement or memory called into question, we tend to believe the accuser and ignore our own judgement. Most of the time, a categoristic doubt of oneself is UNFOUNDED.
End of rantI'm really sorry to hear that all that happened, dear and I wish we all here could reach through and smack someone. Take care, and no, I still don't think you are stupid. I just wish you had better In-laws.