Veto power is absolutely a norm for some couples. I get that the OP doesn't want to have it at this point in her life. I merely suggested it for the future because I can't imagine she would skip having children with K just because some people in a forum thought she should, and it is possible that K has an issue with retaining relationships with people who don't respect his other partner, the OP. (I don't think we know enough about him at this point to really say that, but it's possible.)
I see veto power as a workaround for people in situations where one partner is too tolerant of partners with toxic issues for their main partner's comfort zone, or has blinders on in general about said issues. It's one way of making the best of a problematic situation. It's not for everyone, certainly, but it works for some of us.
Female, married just about forever to Scout. My boyfriends are E. and C. Both are married, and C also has another lover, J.