Suggestion given here:
When recording the couple's information, do not enter a marriage date or place. If you want to indicate the couple never married, enter that information in a note.
Does this help?
As 'Anne' has already proffered ...
No big deal ...
Just leave the "Event" as "Blank" (ie. NOTHING).
There are many such "Couple" Relationships in "Family Tree" of "Family Search".
But, there are two (x2) things that you SHOULD "Also" do ...
Firstly, ADD "Notes" and "Reason Statements" everywhere you can to the effect that they were, "Never Married"; and, "Never Lived Together".
Secondly, in the "Other Information" Section, select "Add Information"; and, go down that 'Drop Down' Menu to the sub area of "Facts"; and, then, to "No Couple Relationships" ... select that.
In the "Reason Statement" add details to the effect that they were, "Never Married"; and, "Never Lived Together".
That way you have 'covered the bases', as best you can.
If it were me, I would even add the SAME, "Never Married"; and, "Never Lived Together", in the "Life Sketch" for BOTH individuals/persons.
I hope this helps.
Thanks to the both of you.