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.