Why???

Why is it that everytime my boyfriend and I get into an argument when I go to sleep I dream of him cheating on me..... I have no idea why I have these dreams but I hate that I have them! Is it cause I lack self confidence? Or that it is one of my worst fears, that one day I'm not goin to be enough.. I don't know, but last nights dream was so vivid I knew who it was with and when he left me... I just need advice