In coronation street how come leanne and michelle dont like each other they used to be friends?

in last week's episodes peter and Simon went to see if she would come back and live with them over the bookies when she came back she asked peter that if she was to stay if would have to be totally honest with her no more lies, he said I told you everything nor more lies, the following morning simon said to Leanne while eating your breakfast you are nicer then the naomi and michelle, Leanne then guessed that something went on with Michelle but peter said that she only worked With him Leanne them met Michelle in the street outside the Kabin and tricked her into telling that she slept with Peter