I have nothing much to add to the advice you already got...your son is old enough for you to have a talk about how you are dad and that you want to be in his life as much as possible, but are limited because his mom moved away. I think you should also consider telling your XW that you prefer for your kids to call you dad and you'd appreciate if she would refer to you, when talking to the kids, as "your dad". Ask her how she'd feel if the kids referred to her as "Dawn" (or bitch) when they are with you and when you remarry the kids will call the new wife "Mom". BTW, I think I hate your XW. She's not a good mother....a good mother wouldn't do this to her kids. I'm glad I never had to deal with an XW that remarried and my kids had a step-dad around.
I'm sorry Kevin. As a guy that worries about how his kids perceive him, I'm very aware how bad that would have hurt.
P.S. Many sports things are now online. Maybe you can find the schedule for his events and practices online.
You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer