Separation Anxiety Help Needed

Any assistance/advice would be much appreciated. My 19 year old gelding is recently (as of this weekend) is experiencing extreme separation anxiety over a mare. I’ve had this horse since before he turned 4, and have known his history since he was a weanling. He is a really good boy, and has always been happy to come in. Generally speaking if I’m out during “normal hours” and call him, he at the least walks to the gate, but generally he trots or gallops up to come in. Until this weekend.
The mare that is now “his,” is the prize mare in the field. She has been in heat, so this is definitely exacerbating the situation. He will now when called, look up and see that I’m there, and then after a few seconds drop his head and start eating, or turn and go towards the mare, and pretend not to see me. I brought him in a few nights ago and had to drag him in, and not allow him to trot circles around me to get away and back to the mare. He has never, underscore, never, acted this way.

I recently got a new mare about a month ago. She lives in his field. She’s not mine, but I’m riding her for her owners until she sells. He was not thrilled with this development. If I go to get the other horse in the field next to his that I ride a few days a week before I get him, I alter my steps, because he’ll here me, and would walk over and stand by his gate wanting to come in, and then toss his head in frustration while he’s waiting. So he’s not a big fan of his human visiting any other horse. To make this already challenging situation worse, the mare, stole his best gelding friend. While he was very attached to him, he never had anxiety leaving him.

The two recommendations I’ve found when searching for help with this are:

  1. Separate the horses. This isn’t an option at our current barn. So I’d have to move him to a new barn. Anyone who lives in Northern Virginia can attest to this, it is close to impossible to find an affordable barn that takes great care of your horse, and is not a killer commute. I’m currently at that type of a barn, and enjoy actually sleeping at night and not constantly worrying that my horse is going to be hurt, not fed, not have water and so on. It is fantastic! So, moving in this area isn’t a great option. And I could move him home, 5+ hours away, where I know he’ll be taken care of… but the gist is, until recently, my horse was very attached to me, and vice versa. I will do this, if it is the best way to keep him and everyone around him safe though.

  2. Make leaving the herd a positive experience. Well, it had always been a positive experience. He’d come see me without having to be drug in, or me even having to go out and get him 99% of the time. He gets tasty hay cubes and is spoiled rotten. He’s semi-retired, and has been for years due to some health issues, so he’s worked when he feels well and only worked hard when he wants to. I honestly don’t know what I can do to make coming in more positive.

The problem is he doesn’t want mare to be stolen, and he doesn’t want to lose his new found “alpha” status. I have no idea what to do, I don’t want to move him… but I will if I have to because I don’t want him to hurt another horse, human or himself. Any thoughts would be much appreciated.