Can i create my own back up iCloud account other than the one my ex boyfriend set my iphone up with?
You can do this by signing out of that iCloud account. Open the Settings.app and go to iCloud. Then select "Delete Account". Not to worry, this doesn't delete any information from your device, as long as you choose "Keep on iPhone" after signing out of that iCloud account. It will display a prompt after you select "Delete Account", and give you the option of keeping iCloud contacts, calendars, and such on your phone. Like I just mentioned, you will want to select "Keep on iPhone" when facing this prompt. After signing out of iCloud, create an Apple ID (there should be a way on the iPhone itself), and sign into it.

As a side note, unfortunately, you will likely have to purchase any music, or apps, again, that were purchased on his Apple ID. The apps that were purchased with his Apple ID will continue to function, but you will no longer be able to update them, and consequently, the need will likely arise that you will need to purchase them again.