Needing space from someone you care about is not the same as not wanting them in your life. But it often feels that way to the person you are saying it to, which is why so many people avoid saying it at all.
Instead they pull away without explanation. They become less available. They respond more slowly. They hope the other person will take the hint without them having to say the thing directly. This usually works worse than saying it, because the person on the receiving end senses the distance without understanding it, which tends to create more anxiety and more reaching out rather than less.
Be honest about what you need, not what is wrong with them
The most important thing when asking for space is to frame it around what you need rather than what the other person is doing. "I have been feeling overwhelmed and I need some time to myself" is about you. "You have been a lot lately and I need a break" is about them, and it lands as a criticism rather than a need.
Even if their behavior is part of what is prompting the request, the framing of the conversation around your need rather than their behavior is both more accurate and more likely to be received well.
Be specific about what you are asking for
Space is vague, and vague asks are hard to fulfill. Are you asking not to see each other for a couple of weeks? To text less often? To skip a few social events? The more specific you can be about what you are asking for, the less anxiety it creates on the other end, because the other person knows what the ask actually is rather than filling in the blanks with their worst assumptions.
Tell them it is not about the relationship
If that is true, say it. "This is not about us, I just need some time to be with myself for a while" is a sentence that removes a significant amount of potential fear from the conversation. If it is partly about the relationship, be thoughtful about how honest you want to be in this particular message versus a larger conversation.
When you need help finding the words
This is a conversation where the words matter a lot because the potential for misinterpretation is high. unsaidit can help you find language for this specific request in a way that is clear about what you need without sounding like a rejection of the person or the relationship.