New horse fretting when mare from other field goes out
I have recently taken on loan (a week ago) a horse that I have been sharing for the past 6 months. He seems to have settled in his new home just fine (only a few 100 yards away from his old home), however, although he is in a field on his own, the field backs onto another yard where 3 mares are kept, he can see them all and stares down at them a lot. He has hacked out with one of the mares a few times so knows her. On Sunday we had issues as we were going out for a hack with this other mare, but when she turned up to meet us he just went lary, rearing up and generally going crazy. I got on him still as didn't want him thinking that he does all that and gets let off, and he was as good as gold on the ride with her, but as soon as we got back to the yards and she disappeared down the track he went crazy again until he could see her back in the field! Last night this mare was going out on her own and has to walk past my field to do so, when he saw her going he just went lary again, galloping up and down the field and calling, to the point where I could do nothing with him but leave him in his field to get over it. He paced the entire time she was gone and only settled when she came back to her field.
I am not yet seen as his boss although he does listen to me and do as I ask when we are out, without a problem so feel we are getting somewhere.
How do I stop him fretting so much when she goes out, it is horrible to see him stressing so much to the point where I can do nothing with him. On the other handI don't want to end up in a position where as soon as she disappears he goes nuts, and I can't do what I want with him because of it.
I know he has only been at my yard for a week so it will take time to settle in, and I am hoping that after a few times of her going out without him that he will realise she does come back and all is well again and he just stays calm in the meantime... is this likely given time?
I am not expecting so much so soon with him, but some helpful hints on how to help him in the meantime would be really appreciated.
His old yard he was in a field with other horses, but he isn't now totally alone so it shouldn't be a lonely thing?
Sorry this is long!
Thanks in advance for any help :)