Major Scobie in The Heart of the Matter by Graham Greene commits several deeds that would be considered sins by the Roman Catholic Church. The first act of his that is technically a sin is usury, in borrowing money from Yousef. Although the Roman Catholic Church no longer considers all lending for interest a form of usury, having gradually softened its stance about lending for interest in the sixteenth century, the sort of extortionate lending practiced by Yousef is still condemned by canon law.
The next major sin Scobie commits is adultery, when, despite being married, he falls in love with Helen Rolt. This leads to the next sin. He does go to confession, but because he refuses to promise to stop seeing Helen, is refused absolution. Despite this, he commits his next sin of taking communion despite being in a state of sin. Next, he commits suicide, which is also a sin.
For type of Catholicism, Scobie seems to be in the English tradition of liberal Catholicism, which was typified by more thought about theology and less strict ritualism than forms of Roman Catholicism practiced in Italy and Spain. However, he is a layperson, not a theologian, and even if he reflects on religious matters, and appears top practice a form of casuistry, he isn't really affiliated with an particular school of theological thought.