The relationship between Eli Goldsworthy and Julia known as Elia (Eli/Julia) ended on the night of April 22, 2009, about a year prior to Season 10. The two got into a heated argument, and when Julia decided to leave, she was hit by a car while riding her bike. The impact killed her and as a result, ended their relationship. Julia's death haunted Eli, and caused him to begin hoarding objects in his room to deal with his grief as he blamed himself for her death. Eli has had a rough time coming to terms with her death.
It is not stated how long Eli and Julia were together, though they did not willingly end their relationship. While Julia was living with him, they were sexually active. As they were fighting on the day of her death, the two never made up, which contributes to the guilt Eli harbors toward his memory of her. Even after a year has passed following her death, Eli is still not fully over her, but is working on dealing with his emotions.
After Julia died, Eli started hoarding.
Julia would stay at Eli's house after fighting with her step mom.
They were sexually active.
It is never explained what Eli and Julia were fighting about before she died.
Reason: After an argument with Eli, Julia started to ride home on her bike, but on the way, she was hit by a car and killed. (It's possible that they were together in Season 9 though they were together before Eli was on the show)