This has nothing to do with your birthday, but it's worth noting that "veto power" doesn't equal "ending existing relationships" power. Veto literally means preventing something before it happens.
My girlfriend and her husband have a veto agreement. But once a relationship is established, that veto power ends. He had the opportunity to tell her she couldn't start dating me, but now he can't tell her that she has to break up with me. That's one reason why meeting a new partner before things get serious is a major part of how they do poly.
Now, it could be that JP and J mean something else by "veto" and that they're just using the wrong word, or it could be that you misunderstood the meaning of veto. I, personally, would want to find out which one it is. I don't think I could be with someone whose partner has permission to send me packing.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker