How can ANYONE hate Jenny???
Jenny loved Forrest in her own way and she NEVER used him...
She never lied or took anything from Forrest for personal gain...
She always looked out for him and wanted the best for him which is why she chose NOT to be in his life because she knew she wasn't the best thing for Forrest.
She couldn't help that from the time they were kids that Forrest loved her romantically, and she loved him differently. Love can not be forced which is why she only saw him as a friend growing up.
She always cared for him... but she knew that they were 2 very different people with very different needs in life... She knew her actions weren't the best choices when she left college, but I think she cared about Forrest too much to expose him to the life she was living and kept her distance... Being raped and abused both physically and verbally by her father (the only family she had) was detrimental to Jenny's mental and social development.. How miserable it must have been for a little girl to have no one to care and love her and to never know that love comes in different capacities not related to sex. She associated sex with relationships because that is all she ever knew..
Her relationship with Forrest was the only innocent and place where she felt cared for and safe.. he was the only man that didn't want something from her or felt like he could treat however he felt when ever he felt.. Forrest treated Jenny with respect and she didn't get that from anyone else in her life.. Every other man expected Sex from Jenny...Forrest just wanted her love... Which is why I think she had sex with him that night before she left after he helped her get clean and off drugs. I think she was so thankful to Forrest for being kind and always being there for her... it was the only way she felt she could repay him for all he had done because in her mind sex was the only thing of value she thought she had to give because of the way her father and men in general had treated her, her whole life. She had NO IDEA that it would result in a pregnancy... she left the next morning while Forrest was still sleeping because she didn't want to take the chance in hurting him later in the future and she knew after that night of making love, that he would have fallen more and more in love with her from that point on. She didn't want to take the chance of breaking Forrest's heart one day and ruining his life. When she left that morning, she had no clue what she wanted in life or what her future held... she knew Forrest needed someone stable and structured in his life and she was ANYTHING but what he needed in his life at that time.
At that moment she knew that Forrest would be hurt some after she left, but it would have still been much less of a heartbreak than he would have suffered had she left in the future when she would have been a fixture in his every day life and he would have been much more deeply in love with her... she also didn't want to see the pain on his face as he begged her to stay and she may haven't been too sure she would have even left that day if she had to be face to face with Forrest when saying goodbye.
The years of sexual/physical/mental abuse she suffered...cemented in to her brain a particular character flaw when it came to men... making it easy for her to take certain paths that women who had normal childhoods, wouldn't think of taking....but she loved Forrest enough and was a good enough person, to know Forrest needed to experience life without her there because she would have only been a distraction to him and she knew she would have held him back in some way from the experiences he needed to experience and the people he would need to meet. She loved him enough to leave even though it would make her life harder. (she gave up living free in a big house, to waitressing living in a small apartment).
She only called him years later when she knew she was dying from AIDS and there wouldn't be anyone to take care of their son "Little Forrest"..... so she did what she thought was best for her son and for Forrest since the only family they had then was each other.