This sentence doesn't need refining - it's "fine" as it is. This is exactly what a native speaker would say. If you are asking us to interpret the speaker's intention, it's probably equivalent to saying "We need some time apart". This is not as final as saying that you're breaking up. I'd say it's suggesting a trial separation.

I'm breaking up with you.

It depends what you really mean and want to say. I'm not a qualified relationship councelor and we don't know the story mate. However, what you wrote is fine . What Derek suggested is straight to the point if that's what you mean and it will save your partner a lot of heart ache.