I could have written your post, I know exactly how you feel. In my case, its my husband who has a job lined up in Perth. He was really up for going as soon as possible, but iv put it off for 10 months, while we save up, get house sorted etc. I change my mind about it every day! My husband will be devastated if we dont go. He'd probably never forgive me. But it will break my mums heart if we do go, we are taking our 3 children with us, her only grandchildren. I am happy with my life as it is. My husband has always wanted to emigrate, I always said I wouldnt. I suppose whats changed my mind is, the lack of opportunities where I live, its a small town that is just going downhill. Theres not much for my kids to do and in years to come, when they leave school, theres going to be very little in the way of job prospects for them.
I think I would feel better about it if we went for a visit first, I feel its a huge risk uprooting the kids and moving to another country that none of us have ever been to before. But with 5 of us its just so expensive and that money could be put to good use when we move.
I hope I can stop feeling so bad, get out there, give it a go, hopefully we will love it! But if not, If im unhappy, or the kids dont settle and want to come back, we will come back. At least we will of tried. Im afraid that my kids and husband will love it and il be the only one that wants to come back. On the other hand, I might love it and they might not. But if we dont try, we will always wonder what if and probably regret it in years to come.
Sorry I havn't helped, but you are definatly not alone.