Why do I keep dreaming of my boyfriend cheating on me?

so I keep dreaming that my boyfriend goes to a party with me and he gets very drunk (wasted) and he cheats on me with a very ugly chick... he doesn't even realize he has done it because he is so drunk but I keep trying to take him home so he stops doing that. After a while I go to my house and he calls me saying that he is sorry that the kissing didn't mean anything and that he wants me to forgive him...

By the way my boyfriend has never cheated on me he did break up for me before but it was always because I was too sad or too paranoid but now, we have been great till I dreamt of this and now I feel very paranoid... and I'm scared it may happen... Please help! why do I dream about thiss!?