Learning songs by ear varies greatly by individual.  But the same things have to happen regardless of the time involved.  You have to learn to pitch match, recognize interval distances, bass note motion, then chords & progressions.

I have tutorials that can help with ear training (aural skills).

Ear Training For Intervals
https://www.guitartricks.com/tutorial/2401/

Ear Training For Chords
https://www.guitartricks.com/tutorial/2414/

Most guitarists learn songs by ear as a practical consequence of learning a lot of songs, chords, licks.  It's a matter of knowledge & practical experience coming together instead of a consciously focused effort.

You learn one riff, lick, song by a certain artist.  Then you notice that artist continues to use variations on those particular riffs, licks, chords, etc.  Then you notice a similar pattern in songs by similar artists.

When I started playing guitar I learned all the basic open chords, some simple melodies & basic scale patterns, then barre chords.  Just like all beginner guitarists! I started to apply this knowledge to learning some Beatles & Monkees songs.  I learned the chord progressions of some songs with a chord book.  And some by trial & error.  Is it this chord?  No, maybe this one?  Yes! 

I learned a certain song used, for example, a D major chord which I played as a basic open chord.  Then I learned more chord voicings.  I gained more knowledge & playing experience.  Eventually I noticed that some of those songs I previously learned used more complex versions of what I had thought were basic chords.  So it was a higher voiced D major chord, and with an ornamental lick!

This is common path.  You learn the basics, apply them, then learn more & refine your playing as you improve.

Hope that helps!