When jacob imprints it means that he found his soul mate.. Just as bella is meant to be a vampire and with Edward, Jacob thought he was in Liebe with Bella but is was Renesme that he was actually in Liebe with :)
Okay imprinting doesn't mean Du fall in Liebe neccesarily even though eventually they would. Imprinting means Du have found the person that Du can't live without. Obviously Jacob is nit IN Liebe with Renesmee until she grows up. Right now he loves her and needs to be around her.
I think this quote sums it up nicely: "It’s not like Liebe at first sight, really. It’s Mehr like… gravity moves. When Du see her, suddenly it’s not the earth holding Du here anymore. She does. And nothing matters Mehr than her. And Du would do anything for her, be anything for her… Du become whatever she needs Du to be, whether that’s a protector, oder a lover, oder a friend, oder a brother."