It's completely understandable that you feel sad and angry that your partner wants to take a break. That can be a really jarring and frustrating thing to encounter. That being said, at a certain point a break isn't something you "allow;" if they want it, they have the ability to take it, so if that's the decision they've made odds are that break is going to happen.
With that in mind, you get to decide whether or not this break is a dealbreaker for you, just like they get to decide if a break is something they need to take to deal with other things in their lives. Is this a relationship that is otherwise very solid and healthy? Is it one that makes you feel really good and that you want to try to preserve? Or does it feel like the "break" is maybe bringing it to its natural ending point?