I am so very sorry to hear this, and am sending hopeful and positive thoughts your way. Everyone who has had horses for any length of time has gone through times like you are having, everyone of us has asked ourselves the same questions about leaving the sport because it can (and does) break our hearts. I won't turn your thread into a "once upon a time I lost a horse to colic" storytime for myself but suffice to say I do understand what you are feeling.
But what is life if not one giant risk? Sure, you can keep yourself safe by not pursuing that which you love but to do so is to deny something deep within ourselves. It denies the thing that most of all makes us human....our innate ability to hope.
More practically, concentrate on now and doing what is best for your filly. Once things resolve themselves, there will be time enough for soul searching. Cyber hugs to you bru, and use this thread to vent away. We are listening.
We grow too soon old, and too late smart.