I can somewhat understand Jenny's plight in season one. She's thrust into this huge, unfamiliar world (Los Angeles), and Tim's busy coaching schedule left her looking for additional attention/entertainment from the only other people she knew in the city at the time. Of course, I'm sure her traumatic youth also gave her an altered view of men and their intentions in a relationship.
I sympathised with her in season one, too. I didn't like the way writing was portrayed through her and how everyone praised her prose when in reality, it was just bad, nothing more than writing diary, really, but other than that, she was okay-ish. Not my favourite character, but she was bearable. But after that,
when her selfishness turned into behaving like a total psycho, I really started to loath her character. I didn't feel sorry for her one bit at the end of S2. And then S5 happened. Oh, boy.