How do you deal with such a painful issue?

i think you are misunderstanding what your bro means. when he says he loves his daughter more then his wife it is a different kind of love. when you actually create a life through your sperm it is a wonderful feeling seeing your own creation grow before your eyes. this is the love your bro has for his daughter. some people do fall out of love just as easily as they fall into love. i believe your bro does love his wife but most couples have a difficult time now a days. because marriage is work. relationships take commitment on both parts. now adays the young adults of today dont realize this thats why the divorce rate is so high,