First and foremost, unlike some fans have speculated, I do not believe Sandor’s father (or grandfather for that matter) was abusive, either to him or to Gregor or to the women in the family. Gregor’s violence, sadism, and psychopathy (if one avoids the literary “he was just born/written that way”) is IMO rooted in a complex of mental and physical issues (seen in the gigantism and the migraines/noise sensitivity); and encouraged by a society that celebrates strong aggressive men with a talent for violence, and also considers women and lower classes to be lesser beings.
And, textually, we know that Sandor’s grandfather was knighted and his father was Tytos Lannister’s squire and also eventually a knight — and yet Sandor’s initial hatred of knights is attributed only to Gregor, and in his childhood he even wanted to be a knight. (Per the text and per GRRM.) And Sandor speaks of his grandfather with respect when relating his family history, and seems to be proud of his house excepting his brother. (“Is being born Clegane a crime?”, using the Clegane arms on his shield, the three dogs story, etc.) So, I feel if there were any truth to the idea that any of the elder Cleganes were abusive, it would have shown in Sandor’s speech or other narration, and as it didn’t, they weren’t.
Also, considering young Sandor’s desire to be a knight, it’s probable he wanted to emulate his father, follow in his footsteps. So, I would think there was once respect there, and almost certainly love. (Especially when Sandor was a very young child.) However… it is without a doubt that Sandor’s father was at minimum negligent in regards to controlling the hyper-violent Gregor, and definitely complicit in the cover-up of the truth of Sandor’s burning. So… there’s complexity there too.
Though it must be realized, Sandor’s father was widowed at a fairly young age (when someone asked where Sandor’s mother was during the whole burning incident, GRRM said she was probably dead), and had three children to manage alone. And here’s his eldest son, his heir, 11 or 12 years old and already six feet tall and inhumanly strong (recall it took three grown men to tear him away from Sandor)… what’s it like to realize your son, your first born, is a monster? That this thing came from you, and hurts your other children, but he’s your heir, he’s still your child… what can you do? This isn’t a world where there’s any kind of treatment for that sort of problem. And so he covered up the truth, he lied, he tried to pretend it didn’t happen. No, Sandor’s father most likely wasn’t abusive — but he was an emotionally compromised, sad man, probably scared to death of his eldest son, with no true ability to protect his other children.
But imagine Sandor, age six or seven — his father was the arbiter of justice in his world, the man who was supposed to protect him, keep him safe, right wrongs — what did this betrayal do to his worldview? Even if Sandor loved him, what was it like to be shown by his father that the strong can get away with whatever they want, that there is no justice, no value in truth? Not just physical, but psychological scarring… a boy’s deep, bitter disappointment in how he once believed the way the world should work (complicated by Gregor’s later knighting by Rhaegar himself) — that’s key to how Sandor Clegane, the Hound, sees the world.
And somewhere around this time, Sandor’s sister was murdered. (Excuse me, “died young under queer circumstances”.) And then, just a few years after Sandor’s burning, Gregor killed their father too. (Oh, sorry, it was a “hunting accident”.) And Sandor left home, that very day, and never returned. (“Not even to visit”, tyvm Ned.) That’s notable, that his father’s murder was what finally made Sandor break away from his home… that there was no longer any reason for him to stay, no hope, no help, no defense at all. It’s no wonder this child (he was younger than 12 when it happened) seized on the Lannisters as a replacement family and became entirely devoted to them. But to them he was only their dog, and, well, we saw what happened when he finally broke that leash.
(By the way, I’ve started to wonder if Sandor initially went to Tywin with some small hopes of getting justice for his father, only to find when he arrived that Gregor had already informed him of his version of the story and was granted the inheritance, etc. One more betrayal of truth and justice…)