How do you learn to navigate a stringed instrument, in tune, by ear? Lots of practice? The cold part about it is, if you practice playing out of tune by rote, your brain will condition itself to believe out-of-tune playing is in-tune. The colder thing is, listening relatively between pitches means that if one pitch is out of tune, the next pitch will be equally or even more out-of-tune, until you hit an open string.
It sticks out in my mind, memories as a singer back in sight-singing and ear training class, how much instrumentalists in the class despised solfège. I had been studying solfège independently with my piano teacher since junior year of high school for singing, and not only did instrumentalists in aural skills hate to sing, since it wasn't their primary instrument, a lot of them really believed solfège was useless in their studies. I even witnessed brass instrumental instructors with performance careers playing slightly out-of-tune at each pitch on concerts.
I saw a violin repertoire tutor on YouTube wisely say that if you can't sing it, you can't play it. I particularly find this crucial on the G string, where it's both a thicker string and hardest to reach. In my mind, I am screaming Fa on that C, and I ultimately know exactly where I need to go.
While not all music is tonal, stop throwing the baby out with the bath water. By the time you're playing atonal music, you will have plenty of muscle memory and improved relative pitch to enable your efforts!
Congratulations to those of you who play in-tune!