To be honest, it depends on your writing style.
First I want to put out there, definitely don't scrap the idea, if you like it, keep it, no matter what. Now back to really answering the question.
Ok, so anyways, you offered four things you could do in your question. 1. Stop writing your current book to switch to the other one. 2. Write them both at the same time. 3. Put the current book aside for a while to write the new idea. 4. Scrap the new idea. I'll just address them all
If by stop you mean permanently, then I say absolutely not. You said yourself that you're in love with your first idea, why would you throw it to the side just because you have a new cool idea? Definitely don't get rid of your first book, especially considering you like it and have already put work into it.
Writing them both at the same time is what I'm doing, but to pull this off you've got to be good at balancing the two. If you focus on one for too much longer than the other than you'll get "rusty" at writing the one that you've been ignoring. Each and every book has to written with a slightly different style, and if you switch for too long, you'll start forgetting the style that you had begun writing in. It's weird and a little bit confusing, but when you start a second book you'll probably get it. So yes, if you balance your time properly, go for it, but if not, just chill with it.
Putting your current book aside might work, now don't get me wrong, you definitely will still get rusty from putting this book aside, but at least in this case, you just get really rusty at writing that book and then you come back, relearn it, and go from there, instead of constantly switching back-and-forth. If you can't do two, I suggest doing this one.
No. If you like your new idea, keep it, when you work on it is completely up to you, but don't scrap it. Keep it and work on it all the way up to the moment that you finish it, or get so incredibly bored of it that writing it genuinely isn't fun. When writing something becomes more like a chore, that's when you know what you're writing isn't very entertaining. I say don't do this one unless you literally have no other choice.
So as an overview. Option two is the best option in my opinion, three comes after two, one after that, and four comes in last. But in the end it's all up to you and your writing style, so listen and take advice from my answer, but don't let it influence your choice too much, after all, they aren't my books.