I think you completely misread Jaye, Christian was *never* Jaye's Boyfriend.
I think you need to replay those scenes and actually read the dialogs a little more closely. Because she very clearly mentions that she felt sorry for Christian after having met him in the school's infirmary with injuries from being mistreated by his father for being gay (recall when she points out 'cigarette burns'). And getting thrown out of his home for it. Then Jaye mentions that she felt sorry for him and invited him to her home to give him a chance to vent about his problems, and then that's when things got 'dicey'.
As for her attitude, I think the story writer really did his homework on the psychological behaviors of people and how some deal with rejection and sexual/emotional tensions. I've personally witnessed similar events before, just not between actual siblings (not that Jaye and MC are actual siblings, I'm not sure how siblings with ZERO blood relations are considered as actual siblings. But for the sake of the story I'll let it slide hehe). And I think she is very well depicted. And her behavior checks-out.
Also, about her relationship with Tara (her best friend), Tara is not gay and neither is Jaye. Again, I strongly urge you to go through the story once more and actually pay closer attention to the dialog details.
as for Jaye being lazy and not working, you really missed alot of text haven't you? because again she points out she worked as a barmaid. I don't know how you can even remotely conclude that she leaches off her parents for money, but that strangely sounds like work to me....
If you play the game constantly skipping ahead by mashing the "CTRL" button, I can understand how you ended up in china using a map for Australia! Just sayin'.