To dream that your ex-girlfriend is pregnant depends if the baby is yours or not. If you dream that the baby is yours, then it implies your subconscious desires to get back with your ex-girlfriend. If the baby is not yours, then it means that you have fully accepted that the relationship is over. You still care for her even though the two of you are no longer together.
To see your ex-girlfriend’s mother in your dream indicates some unresolved issues with your ex-girlfriend. You are wanting to reach out to her mother in order to get through to the ex-girlfriend.
Dreaming about your current boyfriend’s ex-girlfriend reflects your own feelings of insecurity. You wonder if you measure up. In a way, you feel that she is still a lingering part of your current relationship, whether it is physical or psychological.
If you dream that you have an ex-girlfriend, but you do not actually have one in, then she may represent an old friend from your past. Alternatively, dreaming of a non-existent ex-girlfriend may be about how you are rejecting aspects of your feminine/emotional side.