ef: A Tale of Memories., H2O: Footprints in the Sand Recommendations
In both a girl is lonely and being bullied by others. A kind boy helps them and then a love triangle shows up.
Though, ef focuses on multiple protagonists, but H2O has its similarities to ef such as characters suffering from a certain "illness", superb romance, very sorrowful moments and love triangles. If you did enjoy ef - a tale of memories (or even melodies) I highly recommend you watch H2O : Footprints in the Sand.
Both has similar storyline and characters - main is lonely, sad, unloved girl and a boy who helps her to find friends or discover the world.
If you like some drama and love in anime you will love it too.
Both very similar character types. The only difference is that the boy suffer from some sort of dilemma. Romantic drama type
Both have a sad turnout of events and then a happy ending, and both are amazing.
Both of them have sad and tragic feeling