Different files but connected to each other

Hey everyone, i got a big problem here and i don't know why. It comes when i finish my 1st file of picture, after exporting all the pictures and sending to my client, i start to create new session and start working 2nd project. At this point, when i import new picture in, it connect to the 1st file i worked, i got confused when all the pictures in my 1st project appears in my 2nd Capture One Session, then i delete 1st pictures in my 2nd session to keep only the 2nd's. After that i open the 1st session, it appears the same way like the 2nd's. I don't know why, this cause me delete the file that i have already edited and i cannot recover them anymore. THIS LEAVES ME IN DEPRESSION, my client wanna have a slight change or anything, i have to do all over again, and both files still somehow connecting each other and they act like an individual file, eventhough i give them two separated name and file address. PLEASE CAPTURE ONE FIX THIS!!!!!!!!!