Hello! According to Scobie's Catholic faith, adultery is a sin. In light of that, his conduct towards his wife, his mistress, and his blackmailer would not be considered moral. His dilemma is that he no longer loves his wife. She is at once patronizing as well as contemptuous of Scobie: she does not believe he has any ability to secure a good future for them both. Although she knows that her husband no longer loves her, she wants to preserve the outward trappings of romantic love. She forces Scobie to say that he loves her and she also expects Scobie to humor her by coming up with the two hundred pounds to send her away to South Africa. Scobie is trapped by the vows he has made to her; he is trapped by his pity and his sense of responsibility, fueled by guilt. He mentally castigates himself that he should have taken the hundred pound bribe by the captain, so that he could have escaped being trapped by the honesty which invariably marks the epitome of every argument with his wife.
The truth, he thought, has never been of any real value to any human being: it is a symbol for mathematicians and philosophers to pursue. In human relations kindness and lies are worth a thousand truths.
One almost thinks that his wife's cruel goading is an attempt on her part to compel a measure of honesty from her husband.
His relationship with his mistress, Helen, is equally troubled. He refuses to admit to himself that he cannot make her happy. She scolds him that his Catholic faith is a convenient excuse for him to have his cake and eat it too:
"You'll never marry me."
"I can't. You know that. I'm a Catholic. I can't have two wives."
"It's a wonderful excuse," she said. "It doesn't stop you sleeping with me, it only stops you marrying me."
His relationship with Yusuf, who blackmails him, is complicated. Scobie is a policeman; his job is to ensure the integrity of the law. Yet he borrows the money from Yusuf because he wants to ensure his wife's happiness. He shoulders the burden of the blackmail as a form of penance. Louise's self-absorption causes Scobie great unhappiness; she remains utterly obsessed with the outward manifestations of their Catholic faith at the expense of the true condition of her husband's soul. When she bemoans the fact that Scobie committed suicide and that it would be no use praying for his soul, Father Rank tells her,
"For goodness sake, Mrs. Scobie, don't imagine you or I know a thing about God's mercy."
"I know what the Church says. The Church knows all the rules. But it doesn't know what goes on in a single human heart."
So, even though his actions fail the moral test, and despite his misplaced pity, Scobie has always felt that he acted out of love for his wife and his mistress. You might be interested to know that the author himself was unfaithful to his own wife. She never consented to a divorce, and he remained estranged from his own children for the rest of his life. It is also worth noting that Greene himself struggled in matters of the faith.
Thanks for the question.