Im not sure how other people feel on here, but I don't think there's anything inherently wrong with still missing your ex. You'll always have those memories and it's ok to cherish them, in that sense, I don't think there's moving past your memories, but imo its only a problem if those memories interfere with creating and enjoying new memories, and if you're constantly thinking of still wanting to be with that person while you're with your current partner, I can see how that may be problematic. Is this the case with you?

As for whether you will know it's what you want. Yeah, perhaps you simply need more time. 1 month isn't that long. How do you feel about the time spent with this person? What do you think of them?

Also, does your partner know about what you're sharing with us here?