>>213788179 (OP)Alcohol. Alcohol was their problem. The of them only got together because they were both alcoholics and then suddenly they had 2 children in a loveless marriage.
If religion was the problem, then Reverend Puddy wouldn't be the most moral character in the show. He does sleep with another man's wife, true, bit it shows he struggles with lust like all of us and that's okay, what matters is his ultimate redemption.
Clay never gets redemption because he's an alcoholic and a sodomite.