But you can still be their anchor * JAM49* albeit at a distance, and as a mother you can still guide them through choppy seas if things get rough. You haven't abandoned them if they are happy about your move, so don't beat yourself up.
For what its worth we moved abroad when our children were university age. Lots of moans about deserting them, making them homeless, leaving them high and dry etc. I did worry our relationship with them might be destroyed, but I always kept the channels of communication open (and that was in the days before WhatsApp or video calls). I count my lucky stars 20 years later that we all now live in the same county, one even moved from London during the pandemic to be nearer to us after we bailed out of the capital leaving her once again without our support. I never ever hear any accusations of spoiling their lives.
Try not to feel guilty, but I do understand how you must miss them. Have a bit of a cry and beat yourself up for 10 minutes, then be grateful for things as they are.