grammar - Understanding "よりを戻す" and "止めておこう"

I don't think us getting together tonight is such a good idea.

やっぱり今夜、よりを戻すのは止めておこう。

I would like to understand this sentence better, specifically the (idiomatic?) expression, "よりを戻す." I will parse the parts I am not sure of below to see if I grasp it correctly:

"やっぱり" "after all."

"よりを戻す" is an idiom(?) meaning "get back together."

"止めておこう" "Should let pass/should let the matter drop/let's quit"

If these are acceptable, how does "よりを戻す" express "get back together"?

And does the おこう in "止めておこう" derive from 置く?

Answer

As you correctly understood, よりを戻す is an idiom meaning for a broken couple to get back together.

[縒]{よ}る means “to twist threads together to make a thicker string.” [縒]{よ}りを戻す literally means to undo this process and turn a string into several threads apart. This may sound like the opposite of getting back together (certainly it does sound like the opposite to me), but I guess that the analogy here is that “twisting” refers to the conflict between a couple, and removing the twist corresponds to getting back together.

おこう in [止]{や}めておこう is etymologically derived from 置く (to put), but here …ておく means “to do … for now.” In this context, よりを戻すのをやめておく means to avoid getting back together for now.