Please be advised that my opinions are based on my interpretation of a Master/slave dynamic and as such may seem a bit harsh. Your milage may vary. Once a slave accepts a master's collar, he/she becomes owned property. The slave only has 2 options available after that, obey or leave.

Your master didn't ask you for permission to get a playmate. He told you what he's going to do. Your voice was heard and duly noted. Obey or leave.