Wotakoi is my top choice, and comes packaged with a top-tier manga.

Tokyo Godfathers also portrays a realistic adult life, for a certain sort of adult anyways.

Easy: Journal with Witch

I’d say it portrays life in general realistically, and that includes adult life of course.

Shirobako is one of the more realistic anime I’ve seen for depictions of real world adult life. Some things are still exaggerated, especially for comedic effect, but the work/stress/organizational dysfunction/interpersonal conflict bits hit decently well.