One of you needs to setup your own icloud account. That will solve the problem. You should have your own icloud account anyways as going forward in the future you will need your own.
One of you should go into settings and find the option to erase all content and settings. This will wipe one of the phones, and then you will setup your own icloud account and the iphone will be your own after that.
No more photos will appear on the other. Keep you icloud account password private and make sure its something you wont forget. Make sure there are numbers embedded somewhere in it also as that will keep people from ever being able to guess it. Read the password rules here on how to create a password: