It is arguably a very uninspired literary device to set up conflicts, but it is unfortunately not exactly unrealistic. Estimates are that more than a third of western society, probably closer to half, meet the DSM-5 criteria for substance use disorder at some point in their lives. Roughly a little less than a third will cheat on their partner during their lifetime, closer to half will have their partner cheat on them. These numbers are after a rough fact check courtesy of whatever Gemini model is in Google search, my own rough sense and knowledge of the literature is just that it's very common.

Uninspired as they might be as literary devices, drug abuse and cheating are common themes in actual human existence.

Not trying to normalize usage in anyway. I just wonder if a behavior is well represented in a society is it still a disorder?

The behavior while under the influence should get labeled but the usage might be normal. People being angry or not taking responsibility deserves a label from the DSM. If a large population is ingesting things this might be normal.

It might be that some sort of intoxication is the normal and abstaining from intoxication is the thing that’s normalized.

> As an aside, same with cheating in movies/series

As an aside from an aside, I find very interesting how every couple of main characters in movies has couple problems (cheating, lost of interest, one of them don't want to engage the other, etc). Taking a look at my list of recently watched movies (including very diverse ones, like Godfather, KPop Demon Hunters, Whiplash, Sunset Boulevard, Up, etc) and I cant't find a single one that we don't question whether the couple will stay together...

Actually, the only two exceptions that I remember are Marty/Jennifer from Back to the Future and Ferris/Sloane from Ferris Bueller's Day Off...

Spoiler: it's not drugs, you have to watch it till the end, and I mean it, really until the final season. I can't say much more than this without spoiling the very heart of the show.

In the final season, Mr. Robot does some fairly ambitious episodes. One of them is a continuous tracking shot (or made to appear as one) that goes through the entire episode. Another one has no spoken dialogue for the majority of the episode. A very well-written show. And yes, you really do need to see it all the way through.