Therefore, is an open relationship a good idea in this case scenario?

No.

And I say that as someone who is a HUGE fan of open relationships. I think monogamy, though I practice it personally, is for suckers. I think monogamy is a broken and useless system.

But you're doing this wrong from the get go.

You want an open relationship? I am for it. But first, you have to read. You are both bred and born in the monogamous world, ergo you're going to have to figure out what you mean by "open". There are about a thousand kinds, none of them are the same, and you're going to have to figure out what "open" means to you two. Read a lot of books, there are hit lists of the classics if you google, and get a sense of what you want out of open. Don't ask, don't tell? Do you want to share a third partner? Do you want an adventure-then-confess kind of thing? Does it turn you on to hear about the girl she went down on last night? Is she reallllly okay with you doing it too, or is that going to be a living nightmare?

ALL UNANSWERED QUESTIONS. Open relationships are great but they have many more rules than closed relationships. Closed relationships are easy (okay, no, but for the sake of argument). Don't fuck/love/kiss other people. Okay. Straight forward, right? You're opening a world where high-level communication, honestly, trust, and sacrifice are a premium to success. That's how it gets done.

You are not actually being asked for an open relationship. I am sorry to be the person to tell you this, and there's a small chance I am wrong, but what you're being asked for is a slow fade. She doesn't want to dump you because she does like you. But she knows, deep down, that this isn't going to last. The open relationship thing is a mirage to get you to a place where you'll fuck someone else, she'll fuck someone else, and then you'll both end it because...well, gee, it just didn't work out. It is dumping-avoidance, not a real plan to keep you together. There's a way to make this a real plan. But she either doesn't know enough to act on it or doesn't want to. And hey, maybe she's just a noob! You're both young....maybe you can bring her on board the education train and actually forge an open relationship that makes you both happy. It's not impossible! Maybe you can both fuck around casually, like it, like each other, and come back together later in life and renegotiate the situation. Crazier things have happened.

But what she gave you, what she offered....that's bullshit. Maybe she didn't know better, maybe it was intentional, I don't know because I don't know her. You do. So talk it out and see where you land.