Most Helpful Girl
Though Minxxe put it rather forcefully and I agree in part with what she is saying, I have noticed that we can associate certain physical characteristics with the all the other real reasons we are not with our partner. I have a girlfriend who was repelled by the idea of dating someone younger, shorter and skinnier than her (which her ex was all of the above). Her fiance is older, taller and no skinny minny. It is quite obvious that she is not with him because of that, but she just could not stomach dating someone that reminded her of her ex. I have other friends who just cannot work up any physical attraction to someone who reminds them of their ex's.
Beyond that, we can tend to date someone who emotionally matches certain traits that may not be what we really need, but make us feel comfortable. I had no idea I was doing that until I finally really looked at it and realized I was initially attracted to men who were as emotionally aloof as my father. Down the road I would lose my attraction but that pattern kept repeating until I finally addressed it. I then had to look for the man who was not clingy but also not keeping his distance.