You are either not over her yet or still seek closure. That or you simply have strong views about 'friends and exes not dating' thing.
Since you asked openly, I would be honest: this doesn't concern you anymore. It's been a long while since you broke up, she's allowed to move on and date, same as you. Although it is kinda awkward your friend wanting to date her, but he hasn't yet, just hooked up; he might also be comtemplating how to approach this with you. Give him benefit of doubt.
In mean time, try getting over it. This is about two other people, one of whom not in your life anymore. Just let it go, not the end of the world.
Good luck. :)