Here's the thing...they're all grown ups. They make decisions that you may not always like or agree with. It is how they want to forge a life of their own.
Just as you are with your new partner. It is a positive to read that you do try to reach out to your boys. For me, my best memories of when I called my late father on Sunday evenings no matter where I was in the US. It was a ritual that we never broke until I moved in with him when he had cancer and passes away two years ago.
Likewise with my mother....I talk with her frequently.
Perhaps you can try this and see if you can establish some type of phone ritual with your boys. Just a thought.