I'm a big fan of Waugh but BR is my least favourite of all his novels. He was a Catholic convert, not a cradle Catholic, so I don't think his aim in BR was to criticise the Catholic church, because his view seems to have been that the church was right and it was the godless, directionless 20th century agnostics/atheists who were wrong. (Later in his life the church started to relax its teaching on some issues and he was horrified. I think the rigid, unbending stance on all sorts of issues was what appealed to him.)
He grew up in the Anglican tradition but his family were not particularly religious. He was not happy as a young man. He felt overshadowed by his older brother, who was a novelist (now largely forgotten, but EW wasn't to know that would happen). His relationship with his father was not as bad as Charles Ryder's but they weren't close. EW got into Oxford but did not distinguish himself there. He kept a diary all his life but he destroyed some of the entries covering his time at Oxford/immediately, presumably because he felt they reflected badly on him and/or he couldn't bear to be reminded of that time.
I'm sure young men at Oxford in the 1920s could have had female company, but they'd have had to go off to look for it, as almost all colleges were men only. EW seems to have had some very close male friends, and was very likely in love with at least one of them. Several of them were as near to being openly gay as a man could risk being in later years.
After leaving Oxford he settled in London, with a spell working at a prep school very like the one in Decline and Fall, trying to work out what he wanted to do and eventually starting to write. It was during this time he married his first wife, She-Evelyn, and it didn't work out at all. They split up and divorced within months. It was in the dark days that followed that he started to think about converting to Catholicism. Then he met Laura, who was to be his second wife. She came from a devout Catholic family and he knew he couldn't marry her unless he could get the Church to agree an annulment to his first marriage. Strings were pulled and he got that. He married Laura, who must have been a woman of superhuman patience to cope with him, and appears to have been as happy with her as he was capable of being, for the rest of his life.
He wrote BR towards the end of the war, ten years or more after that tumultuous time in his own life. Bearing in mind he and the rest of the world had just been through six years of turmoil, the overwhelming mood of the book seems to me to be nostalgia for a vanished age. But also, as I said at the start of this long ramble, he had an uncompromising attitude to Catholicism. Charles resembled EW himself in many ways, but of course Charles never found his way to the faith, so EW has little time for him. I don't think EW liked himself much either, frankly.
Maybe I should re-read it.