Still in a relationship but changes fb relationship status to single?

My best friend is a little bit worried because her partner of 4years, who she has been in a serious relationship with (living together) changed his relationship status to single even though he is still living with her and still in a relationship with her?

He has there's nothing to it but she thinks there is?

I don't know what advice to give her! They haven't been fighting at all! They love each other a lot and have known each other for 15yrs.

Why (do you think); Would a guy all of a sudden do this?

Still in a relationship but changes fb relationship status to single?
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