Hilary Duff "Love life to split up"

Joel Madden and Hilary had enjoyed their livings together having a crush on each other and had continued the reloations for two years. Recently they have declared the split up.
Reasons vary from magazines to magazines and sites to sites.
Some of the reasons that have been claimed are ..
1> Joel is 27 and Hilary is 19.

Most of the sources talk about this very reason for their split.But if so why had they continued their relations for the past two years. That's a question from fansofhilary.co.nr ?