Why has my dog started barking when i leave?

She’s scared.

This website says that separation anxiety might be causing it. (There’s also info on how to handle it.)

she misses you?

Most certainly is separation anxiety. There are many ways to treat this. I would suggest talking to your vet or an animal behavioralist. Is this something that developed out of the blue?

When a pet’s behavior has changed, the first thing you should do is see a vet.

Has your routine changed? New additions to the household? New animals in the neighborhood? I don’t think your dog would all of a sudden develop separation anxiety. There might be a trigger.

@hawky454 yes it did, never happened before

Maybe she actually waits until you are gone to bark.

“she has never done this before, now my neighbors tell me when i leave she continually barks”
It could also be that she did this all along, but your neighbours only now told you about it (for whatever reason).
That doesn’t answer your question i’m aware, but it might clarify things.
If you assume she just started this behaviour, you may look for (recent) reasons for that behaviour, but if she barked after you left for years already then there are maybe no recent reasons for it.
If that makes sense.