They didn't have a veto agreement. She just decided she was not okay with me, and told him he had to choose: her or me.
I've cut all contact with him. I am working on not settling for things that I don't actually want, and at this point in time I have zero interest in being his friend. Without the hope or desire for the return of our romantic connection... I'm out.
On the plus side... This experience (which was AWFUL for a few days, but I know better for me in the long run) has made a few of the people I've been talking to from OKCupid and the like revisit their agreements with partners. Apparently seeing how ridiculous a veto/ultimatum situation is from the side of the person being dumped makes people realize how terrible it really is. Maybe my pain will save someone else from this fate in the future.