Separated/wife moving away with daughter

[whoppa]

my wife told me may 14th that she is moving to delaware june 1st. She is moving in with a guy that she met online(yahoo). she plans on taking our daughter with her. Basically, she has said that i would see our daughter when she drives up to visit her family. What can I do to stop her? its crazy to take a 41/2 year old to a place where she has no family, and away from her father. My daughter and I have a great relationship. My wife has used her condition(MS) as an excuse for everything and I dont see her changing now. Please someone help?