If you haven’t seen it, I highly recommend it. If you have, it rewards rewatching — especially to notice how Summer’s actions are more honest than Tom’s narration admits.
Would you like a full plot summary (spoiler-free or detailed), or where to stream it currently? 500 summer days full movie
I think you're referring to (often styled with the parentheses). It’s a 2009 romantic comedy-drama directed by Marc Webb, starring Joseph Gordon-Levitt as Tom and Zooey Deschanel as Summer. If you haven’t seen it, I highly recommend it