Hold it! Do you understand the shock value of throwing out the "I need a break" phrase has on a relationship? Be real here!
This goes both ways, more often than not when those words are muttered the person being spoken to is always caught off guard. If you think about it there's usually a long conversation once these words are spoken.
On the other hand, you have been pondering this over a period of time, yet you never said a word. Your mate has no clue what your thinking. So you throw those words out there and expect your mate to just sit there and say, "oh sure no problem."

Just like that he/she is expected to understand.
ARE YOU FOR REAL? 
Your mate doesn't know whats on your mind. It comes off as possibly a major step towards a permanent breakup.
The bottom line is when your on the recieving end of "I need a break" you can't help the feeling of despair. You can't help wonder what you did wrong, where did I fail?
I have a few questions on this matter. How long is this break supposed to last? What is the mate supposed to do while your taking your break? What if someone else steps in while your taking your break?