Your Messenger message:

"hi sir, what does it mean when someone who died exactly a month ago appears on your dream saying that he's going to take you with him and will be wearing the same white dress as he does?"

My reply:

Hi _________________!

All it means is that you loved or admired that person, consciously or not, and that that person had an impact on your life greater than you think or are willing to admit, and that, when he died, a part of you died with him.