Oh Op, I know the feeling well.
I was in the same boat as you a couple of years ago when my eldest DD made the announcement she would be leaving to live overseas with her boyfriend. Like you, it was for work and a great opportunity that couldn't be passed up. They were so excited about their new venture but it made me want to die inside. Although I NEVER showed her this, I just mirrored her excitement but god, waving her off at the airport, was one of the most difficult things I have ever done and I honestly thought my heart would break into a million pieces.
My DD and I had a very close mother, daughter relationship and she was my best friend too in many ways. She lived at home with us before the move also which was doubly hard.
I won't lie, I was filled with sadness those first few weeks she was gone. I could barely go into her bedroom.
We kept in touch via regular messages and Facetime calls and over time it got easier.
They have their own lovely house now, and it hurts sometimes as her boyfriends family live close by so they do lots of things with his family, and his Mum regularly pops in and they go to hers for BBQ's. Things that I always assumed we would do. And I know I will feel it more when she has children and I will be the 'long distance Nanna'. That does make me feel a little sad but ultimately I am genuinely really happy for her and I love how happy she is and at home she feels there.
She has a fabulous boyfriend and they are planning to get married in a few years time. They have great jobs, she has made a ton of new friends and she has made a fabulous new life for herself. She kept in touch with lots of friends from here and she still meets up with some of them on the occasions she comes home to visit.
We take it in turns to go and see her, or she comes to us, and without fail, every week we have a massive facetime call catch up as a family which has become one of the highlights of my week.
I honestly never thought she would move away from family like this. When I envisaged my children as adults, it was never in circumstances like this. I always pictured them close by. She was always such a 'homebird' and was one of those children who would get homesick on school trips or sleepovers. But it is what it is. This is the choice she has made for her life so I make best of it all and ultimately, if she is happy, then I am.
Please just try and be happy for him, even if it is killing you inside. He will thank you for it in years to come. Crying and getting emotional and making it all about you will make him leaving feel much harder and he may even feel guilty. Give him a huge hug, wish him well and plan your first Facetime call. xx