Ah, Cali... I'm soooo sorry to hear this. I know how very much you love your babies...
just know that the guilt your feeling is a normal part of grieving. Doesn't make it any easier but it IS normal. You and the DH are GREAT pet owners. I have no doubt that your animals feel loved at all times, and taking time to do things you love does not make you any less of a wonderful pet owner.
Animals are very, very good at hiding illness... in the wild it's survival of the fittest, so they typically DON'T give any indication of an illness until it's already too late. I've been thru this same thing. My baby had fatty liver disease and was riddled with cancer... never knew it and couldn't tell until it was far too late to do anything.
Right now, take what time you need for you. Be with your pets if that's where you need to be. There is no guilt in not cycling and taking time off if that's what is best for you now. Hugs friend... I know how bad it hurts and how damn unfair it is...
There is a fine line between "hobby" and "mental illness".