In a way I think that your husband is being a littel inconsiderate about the fact that you have a son whom you still NEED to see and be involved with. So it's not something that should weigh on your heart but his.

Well, I can understand your feelings, and the difficult decision that you have to make.

However, it is not impossible to keep the lines of communication open between you and your son, and also at his age now, he is likely to become more independant, and feel less and less like he needs his parents around. You have to also think of your own long term future, and the support from your own family will be invaluable.

Sit down and have a serious talk with your son, let him know that wherever in the world you are, that you are always there for him, always.

I don't know about you, but if I were you I would not move. I know your husband and your marriage is important, but it must always be the kids who go first.

It only takes one time to do things right with children. You would think I'm very close-minded, and probably very conservative, but actually I am only conservative in this area.

I would die being away from my child, my child will always be more important than the president, the pet dog, the husband.
It was your son who came first girl, before you had your new life with your new family there was a time when he mattered more, try not to forget that.

I am sentimental in this area because I was a single parent for 4 years with my daughter and we were very close in that first 4 years of her life. Until I met my present live-in partner and things started to get serious with him, I vowed to myself never to forget who comes first, and who came first.
It is very hard, I know, to draw a line between your husband and your child, and I struggle everyday and everyday I have regrets, but I will never ever forget who came first, who had my heart first.

This is probably not very sound advice, however, it is how I feel about the matter.
I can see your dilemma, I hope you will have guidance and will come up with the best decision by then.