Both Vicky and Suni (Avoiding Shauna) have happy endings as well, have you seen those? It easily makes up for the bad endings!
You have to actually visit her apartment to continue.
If you go to like the city center (Sorry haven't played in a long time) Its like where the shop is. If you go to the right you should see the aprentment complex. Click on it to visit and select her floor. Cant remember what it is but if you try them all it will only let you choose hers. Theres not many...Hope this helps