Where can i read Love Story by Erich Segal online without downloading?

I don't believe you can, because of copyright. Erich Segal is still alive, you know. Take a look FE @ Gutenberg project - the most free books there are by authors who died long ago. There may be some new ones also but in this case the author himself has to release it.
So you have to wait 30, 40 or 50 years, purchase yourself a copy, or - which obviously is the best solution - visit your local library.