I am so very sorry. As I sit and read this with tears in my eyes, I know and feel your pain. When our furkids no longer have any quality of life left, it becomes our responsibility to let them go... our feelings do not enter into it, but our love for them to end their suffering does. My cocker who had been through so much with me had congestive heart failure and made it 10 months with meds... finally decision day came. My heartache was tremendous, but I stayed with him till last after last breath. Still hurts... 3-1/2 yrs. later.
Wishing you the strength and courage to do for your baby what is best.