So I decided to change my strings and treat my fretboard. As I’m putting the new strings on, the nut just… fell off.
I laid it back in place and put the strings on, everything seems fine. But should I eventually get some kind of glue or something to permanently affix it? Is there a special glue for that?
CA glue (super glue) is a better choice in my opinion. Wood glue will work but CA glue has very little sheer strength. Which means that when you need to remove the nut (replacement, filing, reshaping, etc) all you need to do is give it a tap with a hammer and it will pop right off, leaving the bone and wood intact.
Wood glue on the other hand has very good sheer strength and sometimes when you try to remove the nut, the glue doesn’t break but rather sticks to the bone and what breaks is the wood.
With either glue though you only want to use two tiny drops. If you have squeeze-out then you used way too much glue.
I have seen people use Crazy Glue. The main reason I don’t recommend it to people I don’t know is because I don’t know their experience with using adhesives; If they get Crazy glue on the finish of the guitar, then they’re done. Almost impossible to fix.
Wood glue has much lower skill level entry bar 
Put too much on, wipe it off with a damp cloth. Easy. So the stress level is very low doing the repair that way.
Both work well.
This is a great point. Also you don’t really need anything to hold the nut the tension takes care of that already so if you need things to be in place add a very small amount. There’s no need to permanently secure the nut, you’ll have a difficult, very difficult time removing it, very, don’t ask me how I know this intimately, lol.
I use super glue too. It holds the nut perfectly, and it’s still so easy to remove when you need to. But what @Barney says about the finish is a good point for sure ! You better know what you do with super glue.
I am so sorry for your situation but your title made me chuckle hard and really needed it. Bless you friend lol
EDIT: When my nut fell off my acoustic guitar I used a file to remove the excessive old residue and used elmer’s glue. Still in its place
My Squier 50s P never had the nut glues in place, but once the strings are on it doesn’t seem to make a difference.
Yeah you don’t even need to glue, the string tension is enough. Some people don’t.
I use a very tiny dot of super glue on the fretboard side (not the bottom), just for convenience. Do not go overboard with the glue; a tiny dot is fine.
This is how they can make a Squier 50s P Bass for $279. No glue!
it depends. often it’s true but not always
Yeah that makes sense, probably depends on the break angle off the nut.
also if we talk about a 5 string bass, you’ll have 3 strings pulling one way and 2 other strings pulling in the opposite way, and the force won’t be equal so the nut can more laterally. a tiny bit of glue would fix that
This happens to me when it gets really cold outside. Not my bass. The bass is fine. It’s just me. 
As has been mentioned, just a couple of drops of Super Glue can clear that right up. 
Call me old fashioned but I prefer to keep glue (any kind of) as removed from the nut as possible! 
I don’t like the idea of hammering it away 
I don’t glue mine in.
Fender style nuts should be tightly fitted to the slot.
If it’s a Gibson style nut, don’t take all the strings off at once.
I took the header of this post in the totally wrong sense, but I’m still really glad i read through it-because i am not sure i could have helped…
Heh.
I might maybe have kinda sorta intended it to be taken that way.
Maybe.
Sorta.
What are ya, nuts? 
