I had my old boy Max put to sleep a month ago. I have another horse & like you found it really hard going down to the yard to look after her.
Yesterday i was grooming her legs and nuzzled the top of my head for ages as if to say 'i'm still here and i love you' - its finally getting a bit easier.
Aw poor you. I do sympathise; it is so awful once they have gone. They do leave such a void in your life, regardless of whether you have other horses or not. I know how you feel and although it is a cliche, time is the only healer.
You made the right decision. I sadly lost my pony in Jan aged 40 to liver disease. He had been losing weight for ages and I put it down to old age and tried every food on the market. He sadly collapsed in the stable on the 8th Jan and the vet came. There was nothing she could do. I feel very sad I didn't recognise there was so much wrong with him after owning him for 25 years. But he was so perky in himself up to the end and I didn't get the "look" in his eyes. But I did with my mare who had heart failure nearly 12 months to the day the previous year. Her eyes "told" me she had had enough. RIP lovely horses.