Oh good for you and good luck OP, plenty of new owners have a “what have I done?!” period in the beginning and come through it. I didn’t think you were in the wrong to send the horse back, but I don’t think you’re wrong to keep him either, if you’ve decided you’re prepared to work with him after all.
My horse took a LONG time to settle - I would say 6-12 months. However, this isn’t usual by any means, and there is a major backstory to his situation. I won’t go into every detail because it would take days, but I’ll mention a few things that might be relevant.
Above all, the thing that solved our problems was getting my horse was well and comfortable. Mine had health issues (luckily resolvable) that hopefully don’t apply here. But do all the normal responsible things ASAP - have the farrier, the dentist, worm or do worm counts, saddle check, maybe physio. A sore horse or a poorly one can’t be a cheerful, willing partner. We struggled to make any progress until my horse felt good, and that took several months.
Other than that, consistent and correct handling made the biggest difference. As I said in my last post, it is worth getting some instruction or at least looking into horses’ body language and groundwork. My horse was never bargey but he was very anxious and spooky - bringing his attention back to me before he panicked was key. He now looks to me when he feels anxious, but he learnt that, it isn’t a magical bond type thing
. I have been around horses all my life and have had tricky/quirky ones before, but I still benefitted from experienced eyes on our partnership, on the ground and ridden. I knew what to do but it was good to have some support and fine-tuning while I did it.
We also really benefitted from palling up with another livery and her horse, who were willing to hack with us and share schooling sessions. Her horse is an older, seen everything and got the t-shirt type. He made a big difference to my horse just by being there and being chilled. However, my horse was never allowed to just follow him everywhere and get dependent, we would ride side by side or I’d take the lead for part of each ride.
Let us know how you get on!