my impression from the first post was borderline personality disorder, as I had a similar experience with someone in the past.
(theres a book called 'I hate you dont leave me' which discusses the disorder) Often one of the parents is absent or abusive. And its as if they are trying to makeup for something missing in childhood - usually theres a string of failed relationship or on again off again relationship with someone (who is usually their punching bag) Although it may not be a physically abusive relationship.

I can see why JustME would also start the thread, even though JustMe probably knows what h/she should do, it helps to talk about it with someone even if its an anonymous forum like the mudcat.

I actually posted as a 'Sad Guest' on a similar situation. I ended the relationship, and am now happily married with an 18month old daughter whos going to be a big sister in november. It did help though to hear all the folks responses.