Well If you watch enough episodes, the love really is apparent. For one thing, they are never ever mad with each other. They insult each other all the time, but no one gets angry, they just say a funny quip back. How many other families in sitcoms can say that? I wish my family was more like that. Al and Peggy always insult each other but they never truly fight, and when one of them thinks the other is cheating on them that bothers them a lot. Neither one really wants to leave or wants the other to leave.
When Kelly wants to leave home at 18 because Al won't let her have boyfriends, he pretty much goes to her apartment and begs her to come back and live home.