Title of a book - Earth invasion blocked by aliens

I’m trying to find out the title/author of a book I never finished when I was in middle school, so around the early 2000s.

In this book, Earth exists as it is today (at least in the 90s, when the internet wasn’t as big yet), but unknowingly as one part of a greater universe. Other planets hold intelligent lifeforms that have varying degrees of knowledge of the existence of these other worlds. They sort of exist as a more evolved form of Earth. You get the sense that Earth is a primitive planet and through time, it will eventually become advanced like the other more evolved worlds.

So at one point, one of these worlds “discover” Earth and want to take it over, but an even more evolved world understands that to take over other planets would not benefit the colonizer nor the plundered. This more advanced world wants to stop the takeover and have Earth remain isolated and unaware of the other worlds’ existence. There is a love element in it as well. One of the beings from the planet that wants to take over earth falls in love with a girl on earth. She may have been a farmer’s daughter? I can’t remember.

If anyone can help me, I’d really appreciate it. I really want to finish this book. I’m pretty sure it’s a young adult science fiction book, but I’m not sure.