I think it's natural to be hurt by what you've described but you have come to exactly the right decision - to widen your circle of friends and keep in touch with old friends, and use any gaps in time to be more productive. A very grown-up approach, and the right one.
It sounds to me as if the two individuals who ignored you / didn't invite you in the past have, for reasons unknown, decided to leave you out of this group. That's fine, they can have their reasons but it is likely those reasons have nothing to do with you personally, and it says more about them. Maybe they feel threatened by you - are you better at the sport you all do? Are you more outgoing, friendly and popular? Are you more attractive? 8 months isn't long in terms of friendship, and often what felt like friendship is just a shared interest and when the reason is gone (can't get together to play sport) the weakness of the bond is revealed.
I agree don't ask to be added. In your position I would play it cool but I might mention I saw they'd met up - saying something how lovely to see each other, must have been great after all this time etc, as though it hadn't occurred to you to even have time to think about getting together, been so busy catching up with stuff etc..
Then play it cool from then on because you have so many other interests and people to catch up with so the general impression they get is you haven't even noticed you've been left out.
And yes, I've had similar happen to me - I think most people have at some time. Good luck.