So so sorry. Such heartbreaking news. My heart goes out to you in this terrible time. I hope your other horses take care of you. He was so lucky to have you take such care of him.
That is a terrible blow having done everything possible and it is utterly devastating to lose a dear friend, especially following the loss of your mum. I am so sorry and hope you have love and support around you now and for as long as you need it.
Utterly gutted for you. Please take comfort that you really did go the extra mile for him. Eventually you will think of him and be able to smile at the good times. Sending a virtual hug.