Basically, from all I've read on Diana, I see a pattern in her life where she never truly learned how to have an intimate relationship. By intimate, I mean a psychological closeness and intimacy like one would have with a best friend. A relationship that has its ups and downs and good times and bad times. The unconditional "no matter what" love kind of a deep relationship.
We see this in the statement made earlier "if you leave me now you don't love me." With this in mind, I think she really saw her father's marriage to Raine as a betrayal as in her father "replacing" Diana with Raine in his affections. The solution was that Raine had to go away.
She never really learned that its possible to love more than one person at a time and that its possible to love people on different emotional levels. A best friend, a husband, a stepmother or even the love of an adoring public. With Diana, this became evident when it became fact that in order to ensure her husband's complete devotion, what was needed was to eliminate anyone else in his circle that detracted from his attention to Diana. She was notorious for sacking staff that were too close to Charles. She culled his circle of friends that had more in common with Charles than she did. Basically, she felt threatened by anyone and anything that detracted from someone "loving" her and when there was conflicts, she eliminated the source of the conflict rather than work out the conflict itself by reasoning, compromises and mature cooperation. It was a lifetime of "If you love me, you will (fill in the blank). Her relationships with people were great and glorious until, for some reason, it didn't suit Diana any longer.
Just as Diana tried to manipulate Raine Spencer out of her father's life, so did the same pattern of behavior emerge with many of Diana's relationships over her adult years. We saw this manipulation of a relationship to the extreme with Oliver Hoare. We saw this manipulation in her relationship with Haznat Khan as Diana tried to manipulate the relationship towards how she perceived it should be. This, I believe, also affected her manipulating stories to sway the press and the public. She became good at it. It was her defense mechanism against perceived betrayals and hurt.
I do believe it was the emotional turmoil that Diana experienced with her father's remarriage to Raine when Diana was 15 that deeply affected her relationships for the rest of her adult life.