To see a train in your dream is thought to represent conformity, and going along with what everyone else is doing.
You obviously feel a pressure to conform to society's expectations from those around you to meet a woman and start your own family with her, and while you have pleasant memories of your ex girlfriend Yvette, this particular relationship will sadly more than likely never be.
By constantly looking for her and not being either able or willing to give her up with both your mind and heart, these memories and your longing for something which will probably never work out in your waking life lie just below the surface of your consciousness, and reveal themselves to in your dreams, over and over again.
Maybe finding Yvette and thereby gaining a greater sense of closure would make these dreams go away by themselves given adequate time, but on the other hand you are the only person who can in the end decide whether meeting Yvette face to face again would either make things better between you with reference to you getting you back together again, or instead make it even more painful to have to face the fact that any relationship you once had with her is well and truly over.
Recurring dreams of any general theme suggest that you are either not understanding the messages they are attempting to communicate, or equally likely you do not yet know how apply the principles they are teaching, in your daily waking life.
Hoping this helps,
eye_of_tiger
