Helen thinks it is her fault that people are keeping away - she said to Kirsty as much, that there was something about her that was driving her friends away, but Kirsty was too busy telling her that she didnt blame her for what happened between them that she didnt pick up on it.
Rob has her believing that she isnt a very nice person, he has gradually undermined her and pointed stuff out to her about her behaviour, and she has believed him because underneath there probably is a grain of truth.
But WHY does she behave the way she does - I dont know too much about her background but it seems that she has always been a bit of a disappointment to her parents, not done thing the way they think she should, and from the relationship boards on here its often the case that a child trying to balance pleasing her parents with their own beliefs and personality can often result in very low self esteem and liability to abusive situations because the parents are over dominant and have tried to impose 'their way' or just 'wrong' rather than allow the child to develop into a confident adult with their own set of beliefs and needs.
Just a bit of armchair psychology, but WERE Pat and Tony quite authoritarian, cold and critical? With bursts of 'how could you do this to us?' if she deviates from their view of what she SHOULD do?