According to TheWrap, the first part of the season 3 ended with the final adoption of Callie after that she slept with Brandon, her foster brother. It is also about a serious medical issue for Stef which developed a conflict with her wife Lena and her mother Sharon.
As for Jude, Mariana and Jesus, all three will also have to face some problems. In short, we are eager to see the end of this season to see how all of this will be resolved.
Season 4 should be released around summer 2016.