A couple of things...I agree with others that jealousy isn't an issue. Likely, the ICU staff isn't thrilled with having to train a new graduate nurse; it can be burdensome even if you are a really fast burner, and it can be a real safety and staffing issue if management starts hiring all sorts of inexperienced nurses into the unit. I know the last 3 ICU's I worked at would not hire new grads. Places that do generally have a really good new grad training program in place and/or really great preceptors that love teaching and are supported in doing that. Not too sure that's what you had going where you were.
Anyhow, onto the demotion aspect. I know that no matter what anyone says here--for a while anyway--you are going to feel like it's a demotion, even though it's not. Not working out somewhere after you've put your best efforts in feels very hurtful and it sucks, and there is the looming feeling that the ICU "cloud" will follow you around to your new unit. Don't worry about the "cloud;" the few people that know you came from the unit aren't consumed by it. They'll just be glad to have the new staff on board, regardless of how you got there. As far as the personal disappointment goes, you are just going to have to grieve it for a little bit, think it over and come to terms with what happened, cry a river if you need to, but then push those self defeating thoughts out of your mind and be done with it. Don't be overly hard on yourself. Really! It sounds like the unit might of decided you weren't going to work out before you even started. Regardless, no one is born knowing this stuff and everyone started out at around the same place. You are actually ahead of the game a little. Being in ICU for a few months will give you a little head start when training on the step down. Also, step down is a challenging place to work but a great place to learn. Learn how to work on a busy step down and I think you can work just about anywhere.
It's cliche but true: doors open and doors close for a reason. One way or another it will work out, and in a relatively short time from now you will look back and this whole upsetting ordeal won't mean a thing. It'll be a blip on the screen. Give it a little time and you & your skills and your confidence will grow and then you can figure out where to go from there.....I wouldn't have lasted 2 weeks in ICU right out of school, so I'm glad I didn't try, quite honestly. I needed to spend some time on various floors to get myself together. Other people head straight out of school into ICU and never look back. The deal is everyone and every unit is different. I've seen awesome, experienced nurses "not work out" in ICU, a number of times. Politics and generally stupid stuff and they were out. Sh*t happens and so you can be reassured that you certainly aren't the first person that has had to deal with such a situation, and you definitely will not the be the last. Let it go and just work to be as good as you can be where you are at. The rest will come. Best wishes!