St. Paul's sentence is
quis nos separabit a caritate Christi? Who will separate us from the love of Christ? In the language of the Vulgate Bible (but not in Classical Latin),
each other is an indeclinable word
invicem. (As in
novum mandatum do vobis, ut diligatis invicem I give you a new commandment, that you love one another).
So in biblical Latin, your sentence would be
Quis nos separabit invicem? You could just use quis separabit? as a shortcut, leaving it up to the hearer to figure out who may or may not be separated from whom, just as the various Northern Irish units have done.
The
se- in
separare is a prefix meaning "apart". It is not the 3rd person reflexive pronoun, and
se parare does not mean the same as
separare.
Se- occurs in the following
English words derived from Latin, among others:
- secret: piece of information kept “apart” from what you’re comfortable revealin
- select: single “apart” from a number of things
- separate: keep “apart” from other things
- sever: cut “apart”
- secede: go “apart”
- segregate: to keep certain groups of people “apart” from one another
- sedition: a going “apart” from an existing government
- seclude: shut “apart
- sedulous: of being “apart” from slacking of
- secure: “apart” from care or worry