"I didn't like how it treated same-sex attraction as a switch you just turn off and on, like the book version of Maurice."
We've done this before...
Same sex attractions were rather common with British boys/young men educated in pubic school system which largely were male only institutions. By time young man reached college age things may have gone on further at Cambridge or Oxford.
Some like fictional Anthony Blanche, Maurice Hall, Lord Risley, and Sebastian Flyte actually end up gay men. Others like Charles Ryder or Clive Durham go out of that "phase" to various extents and go about their lives.
Lord Marchmain's mistress Cara has both Sebastian's and Charles Ryder's numbers not long after meeting them. She tells Charles Ryder this "English" with their same sex love among young men is a nice thing, if it doesn't go on too long. Cara notes the Germans are same way, but of course French and Italians are not being Latin cultures.
Anthony Blanche also sees which way things are going, and tries to warn Charles Ryder. AB sees what Sebastian Flyte is likely to end up as, and that Charles Ryder is not his man.
Evelyn Waugh knew very well what he was writing about, as good number of set he ran with at university or otherwise knew were some of the great British homosexuals of the era. Good number "turned their same sex attraction on and off", by marrying and having children/family life; but still now and then having a taste for a man if not running off for weeks on end with one.
Keeping up appearances is not just a snappy title for television show, but was (and still is to some extent) code of conduct for British middle and above classes.
What people get up to behind closed doors is largely their own affair, it is when things are made public and result in scandal that society closes ranks. So gay men (and lesbians) often did have to turn their attractions on or off as situation warranted.
Everyone knew what Lord Beauchamp got up to; it was only after scandal broke he suffered harsh punishment