In a marriage each spouse covers the other when there's a split with commitments like Halloween and poorly timed hockey games. In a divorce and separation these needs have to be broached ahead of time. Setting boundaries, like you did, is a good thing even if it makes you seem like the bad guy.
It's one thing to be asked, another to be told.
Instead of feeling manipulated, look at the big picture.. and see what works best for you, your boundaries and your children.