Son taking his first extended trip with his father...?

Well you cannot control what your ex-inlaws say to you son or how your ex-husband will act on anything they say. You can however tell your son that no matter what anyone says about you or him that you love him with all your heart and you will always love him no matter what. Look him right in the eye when you say it. You don't have to sit him down and have a serious talk with him just say it in conversation while you are eating supper or hes doing homework or something like that. Maybe put a note somewhere where he will find it halfway thru his time with his dad and you could call him every night before bed time and talk to him a few minutes while hes there.