You can get married pretty quick in the game if you focus on it. It really depends on what you want to do and if you want to do everything. You can collect all the artifacts and minerals for the museum, finish the community center/jojo mart, become friends with everyone, get all the animals like the dinosaur and blue chicken, collect all the rare paintings, catch all the fish.
But once you feel like you're done, you're done. I think I'm pretty much finished on my current run, I'll probably pick it up again in a year or two and start again.
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https://imgur.com/g8JFMhA