You can't find the IP address - even for Google it would be a monumental task (searching through the logs, that probably have a few thousand connections every second, for that particular connection).
As B. Diddy said, if you don't use a totally random, and different, password for each place that needs a password, you're risking someone finding one of your passwords and using it on other sites. All they need is your name on Facebook, and they can see what you're doing ("Oh, we went to this fabulous little place last night called xxx" - now they know that about you, and if you and your boyfriend get up to dance, someone snatches your phone out of your bag, installs a spying app ..., you know the rest.)
At the very least, use an app like
Keepass2Android Password Safe on your phone (there are versions for Windows and Mac and iPhones too - keep the password file on the same cloud account for all your devices, so a change in one device gives you that change in all your devices) and use at least a 20 character password - a different entry for every single thing that needs a password. Let's see him try to figure that out. asfkjhgf8h4bwef89lkj isn't too easy to guess. And if he somehow does, that's only for one app, none of the others use it.
Then change the password for every app and site you use (enter it in KeePass, let it create a password, set the password generator to 20 or 30), as you get to each one. A few extra seconds the next time you come here (if you register) and he can hold a gun to someone's head and get your password to this site - and it's useless to him, except for this site.