I am so happy for him and for the great opportunity he has. Yet, I know I will miss him. Even though I haven't see him as often as I could or should, I have always known he's around. Thank goodness for Facebook, Twitter, cell phones, texting, and the US postal service, we'll still be able to keep in touch. I imagine we'll probably keep in touch even more than when he was here.
He's taking the new job because he says that he doesn't want to look back in a couple of years and regret not having tried it.
It's funny because this is the same thing I used to tell my students. "You don't want to look back on your high school years and regret not having done your best." It's important to try new things, to do your best, to jump at opportunities when they are offered to you. You never know how it will all work out unless you try.