My best friend (girlfriend) passed away a few years ago and I've had several dreams that she's really not gone. She just shows up and I'm wondering where has she been and why did she pretend to die.

im not an expert by far, sounds like you havent really excepted the fact shes gone, healing comes in time, but feelings sometimes dont heal. sorry for your loss my friend.

It's very common to have dreams about deceased people.

The person is still alive in your memory, and so can be alive in your dreams.