Is this manga already completed or there's volume 3 coming up?

it's complete. there won't be a 3rd volume, author already confirmed that.

with that said there is a 12page booklet that has not been translated to English called "穢れのない人 後日譚 Jam" which shows a bit of the after story while Kiba is in prison and Aki decides to wait for him. other then that there won't be a 3rd volume.

So it's more like an extra I guess, anyway thank you so much for the info my brother