I am in the same position as you. DS15 father lives on another continent (not Middle East though) and he visits once or twice a year. His Dad is wealthy, has a new wife and DS has two half brothers over there. He lives a life of privilege over there. We are not badly off (comfortable in a nice house, DP and I both have good jobs) but we can't compete with his Dad's life over there.
DS is adamant he is moving over there when he has finished education. Luckily his Dad is onboard with him finishing his education over here, so for now I have him until 21, all going well.
It's so hard to think that as a mother you have put in all of the hard work, made all of the sacrifices, been there regardless, and they are happy to just drop all of that, seemingly without a thought. Interestingly DS says exactly the same as yours, that he feels now he needs to make up time with his Dad as he's been with me all the time so far.
I struggled with it with DS, but I have rationalised it by telling myself, he could have moved away after school or uni anyway (my DB live in the US).
Do you think there is anyway you could persuade him to continue to 18 in school or college? By then he will be that little bit older and hopefully more mature. Would his father support that?