The adjective estranged suggests a loss of affection, a turning away from someone. When a couple separates, we often refer to them as estranged — or no longer together.
The word estranged is an unfriendly word with a negative connotation. The word strange within it seems to suggest an alienation of affection, and that a loving relationship has not only soured, but turned distant and even somewhat hostile. While the word is usually used to describe a human relationship, it can also refer to a political situation where nations that were once allies develop conflicts and become estranged.