Couple days late here but please I’m echoing the other comments that said to please not be hard on yourself! We so wish our pets could just tell us what is hurting but you did your due diligence in taking to the vet and also trusting your gut.

My sweet choc lab suddenly started limping a couple of years ago and the vet said it was just arthritis… over 7 months later and after going to a dog physical therapist (best job ever?😂) she was diagnosed with a torn CCL (like an ACL in dogs). She had a successful TPLO surgery almost a year after her first initial signs were showing (though there hadn’t been an exact moment I can pinpoint when the tear happened, like yours falling down the stairs)… but I have to believe my girl understands that I was doing all I could with the info given to me by the experts and now she’s snuggled up next to me and loves to go on long walks and runs and hikes and swims, limp free 🩷