Question is the 5th vol.the last one of this series? I'm quite dissapointed if so :/

I don't think so. According to this it's still ongoing. https://www.mangaupdates.com/series.html?id=97317

Hmmm the volume I bought yesterday says at the end of the story "end", no to be continued and the story seemed to be finished too, that's why I was confusedΣ( ￣□￣||)