If your iphone is jailbroken there are a ton of ways he could be doing it, so my suggestion would be to restore your iphone so that if he has a spy application installed it will be wiped out, and change all your passwords and everything that has a password... and if you require a jailbreak to have an unlock you can do it yourself it is very easy just do a search online..... Gauranteed to stop the snooping....
He probably has the password to your email account or he has included himself as a hidden CC or BCC on the account. I would change the password.
may be a keylogger on your system. There is no way for a person of that caliber to hack into his ex's phone or computer if he can really do it.
He is able to do this purely because your iPhone is jailbroken. He is using a nifty little thing called OpenSSH, which makes it incredibly easy to access a "not so computer smart" iPhone owner's private data. All you need to do is hook you phone up to your computer and hit the "Restore" button, once you do this your phone will be secure and there will be no way for him to access your information save physically having your phone.