In order to continue building our (mutual) confidence, particularly after Pie struggled a bit yesterday, I took him for a morning ride by himself. This didn't deal with the specific situation that has troubled him - separation from Scout on the trail, but he did have to leave the barn with the other horses in turnout.
I did give him about an hour in turnout before we rode. He was by himself - the other horses weren't out yet, except for Dawn in an adjacent pasture - and he only called once, and otherwise busied himself with eating. After I was done with chores and cleaning my stalls, I brought him in and tied him outside the barn while I got my riding stuff ready. Just then, Jill arrived to feed the other horses and turn them out, so I ended up saddling just as all the other horses were led by him to turnout. He dealt well with that - he did some looking but didn't fret.
We went over to the mounting block and I got on - he's great for mounting and stands perfectly still on a loose rein until I ask him to move off (it's wonderful to get a horse from someone who cares about things like tying, standing for mounting and good ground manners). I asked him to move off down the trail - he was reluctant but did what I asked. We trotted a bit from time to time, but mostly walked - I wanted his energy level to stay low since he was already pretty much on alert. He was clearly thinking about the barn the whole time and kept turning his head in that direction, but that's all he did.
When we got to the area where the chickens and turkeys are raised - they're a ways off the trail but quite visible - Pie suddenly halted and went into "alert posture" - head high, staring and sniffing the air. I noticed some of the tall grasses to the side of the trail were moving and there were soft rustlings - clearly something was in the grass. It turned out that several chickens had gotten out of their enclosure and were foraging (invisibly) in the grasses. Pie found this alarming, and although he didn't want to move forwards past them, he didn't do anything but stare. In many horses, a full alert is often immediately followed by a spin and bolt. Good Pie! I didn't want to force him by them since I want him to do what I ask willingly because he trusts me, so I dismounted (nice that he stands well for this too) and undid my lead rope (which was tied around his neck) and led him by the Scary Birds In The Grass. Since he leads really well - I've only had to slightly refine the skills he came to me with - this went really well. If a horse leads well, sometimes have the person in front can be a confidence booster. I told him what a good brave horse he was.
We led to a large boulder that was handy about 50 feet away, and I remounted and we keep going. I did lots of singing/talking to him and praised him frequently. We got to observe several groups of kids riding their bikes down the street - he was on alert again but just watched. He was a bit more anxious as we neared the barn, but slowed when I asked. There was one head shake/toss/forward surge, and I did an immediate small circle to tell him this wasn't what I wanted. When we reached the barn, I rode him past it and down the trail a little ways in the other direction, then stopped and dismounted. I led him back and tied him for a bit while I put my stuff away.
Charisma's owner has kindly offered to do some together/heading apart work when we're next both riding together. I think his biggest issue is with leaving or being left by Scout, but this sort of work can only help. I've also decided to cut the Ultimate Finish out of his diet (I'd started adding it to get some weight on him) since I think the extra concentrated calories were amping him up a bit, and will increase his nighttime hay.
When I turned Pie back out, Scout was drinking from the trough, and Pie drank with him.
Very good Pie! Every day, we keep building our relationship and dealing with various situations together, and any issues we have will be resolved over time. I'm going to have this horse for many years, and it's a good relationship where he'll willingly accept my leadership that will get us together through any difficulties we face.