What is the meaning of a dream of my boyfriend's pregnant ex girl friend moving in with us?

The dream indicates that the influence of the ex girl friend is interfering with the present relationship. The influence need not come from the ex herself, but could stem from the dreamer's own resentment, jealousy or insecurity. Similarly, the dream could indicate that the boyfriend remains too attached to the ex. Either way, the dream is notice from the dreamer's own mind that all is not well in this relationship.