Your custody battles do not have to roll over into this new baby. This is potential to make an awesome close friend (the mom). The best thing there, if your worried about more custody battles, is communication and compromise. If your son can't come with you, you could also make sure he has contact with his sibling through Skype and the phone. I feel if you put everything you have into letting them both know you will love them, be there for them, be involved as much as possible with them, and that neither one is more important to you than the other, than you have done the best you can and nobody can ask more of you than that. Just don't let being in another country keep you from contact.