do 당신 remember? erza always tells that living proves that your strong.... but during that episode where simonn was killed, erza stood in front of natsu to protect him from jellal's attack, so she was ready to sacrifice her life ...... according to her not trying the best to live but ready to die is a sign of weakness... so when jellal attacked, simon came in front of her and died to protect her.... if she hadnt stood still but fought jellal,simon wouldnt have died.... so she states that because of her "weakness" simon died..... hope 당신 understood :)
and as for episode 154 , it did prove to each other that they liked eachother, but they werent really ready to have a relationship at that point of time... though they didnt convey it through words, they conveyed it through their action
