How to respond to "U deserve better"?

Read the rest of the message before you think hard about this phrase. If she names a specific thing, like plans falling through, slow replies, or feeling like she's doing all the work, then the line is a summary of a reason she already has. Take the reason seriously and don't argue with the summary. If the message is vague and the phrase is the whole message, she's probably leaving the door open a crack. People who are sure they want out usually say so in plainer language. The vagueness suggests she's either not sure, or she's trying to be kind and avoid a fight.

Also look at how long you've been talking and what you've actually done together. Three weeks of texting with one date gives her very little to be sure about, and she may simply be done before anything has formed. A longer history with a sudden shift points to something specific happening on her side. Asking about that is more useful than guessing.

Three kinds of reply fit this situation. The first accepts the ending plainly. You say you hear her, you're not going to push, and you wish her well. Keep it short, with no questions and no request to reconsider. It works when she's clearly decided, and it keeps you from looking like you can't take a no. Leave out any line that starts with "but" and any mention of what you would have done differently.

The second asks one open question about what she meant, like what has made her feel this way. It fits when the message felt half-finished or when you think there's a fixable problem. Go with a short acknowledgment followed by one question she can answer in a sentence. Skip the list of your own counterpoints and anything that reads as a plea.

The third is a light, brief reply that gives her an easy exit or a way back, like saying you appreciate her being direct and you're glad you met. It works when you want the conversation to end cleanly with the door unlocked. Leave out any hint of sarcasm, and don't wrap a jab in a compliment.

Answer the same day if you can, but don't rush a reply that makes you sound stung. If her message arrived late at night, a reply the next morning reads as considered and calm. Don't leave her hanging for more than a day, because silence after a message like this tends to look like you're deciding whether to contest it.

If she replies with something short and polite, that's the end. Send a warm one-line goodbye and stop. If she asks what happened or wants to talk, answer that one question honestly and briefly. If she doesn't reply at all after your acknowledgment, leave it. One follow-up a week or more later is fine only if you have something real to say, like a real question or a reason you enjoyed talking to her. Stop after that. Repeated messages after a clear ending are what get you blocked.