Double texting a girl is considered to be very bad as the double texting the girl can come across as you being over desperate or overly eager.
Double texting girls is often seen as a negative thing in the dating world.
Instead of double texting a girl it's better to wait for a response from the girl before you send another text to them as it's respecting the other person's space and time.
Double texting is also seen as a perception of neediness and makes you seem overly invested or anxious for a response.
Double texting can also make it appear like you're being pushy and not respecting the other person's boundaries if you text them again before they've had a chance to reply.
However in some cases it can be okay to double text but the context also matters when double texting.
For example if you're in a casual conversation and are just trying to keep the flow going, then a second text or double text can be okay.
Or if you need to clarify something that you said in your previous text, then a follow up text message is acceptable.
If you're waiting for a response to something important and you need an answer quickly then a double text can be necessary and okay.
Double texting however is not recommended upfront in a relationship.
This is because double texting upfront in a relationship is disrespectful and shows lack of self-esteem.
It's also not attractive to double text upfront in a relationship and can be suffocating.
The double texting also implies the person is not doing enough.
Later in relationships though, when there's commitment, double texting is okay.