What's for you won't go by you - very popular here in Scotland are the pps who posted it also scots?
It's the "sliding doors" theory really, if you were meant to be in that relationship, that job, that home...it would have happened for you.
This too shall pass - applied to good and bad. Nothing lasts really. Simple but effective and has helped me through as pp said everything from physical pain (from simple headaches to an ovarian torsion) and emotional/mental - I have severe ocd, agoraphobia etc and it helps with the less anxiety inducing things if not the major ones, although I'd very much like this current very bad bout (almost 2 years housebound) to 'pass' soon please universe?
In your case - you won't always feel like you do now, feelings pass, you move on without really trying it's natural. In 6 months, a year, you'll fear completely different and this time will be a mere memory.
If it wasn't right, it was wrong - can apply to relationships, jobs, all sorts.
When I was younger I was very bad at leaving jobs if they weren't working out, it felt defeatist and especially if I can't quite put my finger on the issue. Then one such time I was discussing with mum, there wasn't anything hugely wrong with the job but I was dreading work days and mum said this to me. That it didn't matter if I couldn't completely articulate what the problem was I was sensing it was wrong for me. I started looking for another job the next day and a few weeks later left for new job. It was like a weight had lifted and it was only then I realised what the problem was - the culture was almost all work and no levity, no relaxation during the work day at all, a totally oppressive atmosphere.
You clearly had good reasons for leaving so that's what to focus on. If you didn't you wouldn't have ended it.