The purpose of Istikhara is asking Allah to choose for you something that you are about to do. Dreams don’t have anything to do with it.
As for your condition, you shouldn’t be attached to the idea of getting married to this brother as he didn’t propose and you can’t sell yourself cheap by hinting to him through a third party. You have to forget this brother and don’t allow Satan to get control over you. The brother is not interested in you and may have no intention to get married soon.
Therefore, focus on what would increase you Iman rather than what would bother your thinking without any result.