'Harem' anime isn't really a thing before Love Hina. From what I've seen there is always a primary pair and there may be a few romantic rivals that could never be believed to have any real chance in the end. Although I've seen people arguing that Evangelion is a harem anime although I'd completely disagree.I'd suggest looking into Rumiko Takahashi's works as she was really pushing the Rom-Com genre early on with Urusei Yatsura and Maison Ikkoku. Otherwise Kimagure Orange Road, Macross and Kare Kano are all pretty well regarded.