Also, more often than not a pair will not stay a pair. Wrasses are pairing fish. The have a harem with usually a dominant male(terminal or "supermale" as some refer) and then lots of females/juveniles.
In most people's tanks the female will turn to a male and if it's a small tank, can be problematic
I have a couple "pairs" in my tank, and the female has not changed yet, but they never swim together. It also happens to be my flames and my pintails. I believe the reason the females have not changed is the fact that there is no reason for them to change. I also have a harem of rhomboids that consist of a terminal male, as alter male, and 2 females.
No harassment or change has happened in probably the 8 months I've had them.