Jen had broken down completely. She had been holding back her feelings for so long they ended up overwhelming her. She cried about the broken relationship that she never really cried for. She cried the tears she couldn't show on her father's funeral, she cried for how wronged she felt when her mother made her out to be an ungrateful daughter.
Lucas' behaviour obviously didn't warrant the reaction she had at that moment but it acted like the trigger that opened up the dam of pent up emotions. She tried to control herself but the harder she tried to do so, the more she would cry.
She sobbed pitifully in Lucas' arms and at this point, he had figured out it must be something else because if it was just him then this would be the biggest overreaction he would have witnessed.
Jen clung to his t-shirt as she cried and before he knew it, his t-shirt was soaked with her tears.