It is very difficult to contemplate a future alone but its also very early days for you, and so very difficult to contemplate anything except getting through the next few hours. -i would say try and concentrate on thinking of the future in terms of the next day then the next week, rather than thinking in terms of a whole life time ahead.
If your home is close enough too where you are staying have you thought about returning in small phases, when you feel more ready -an overnight, then a weekend for example -so you wont be alone for long stretches of time or would your sister stay there with you for a while. Take tiny steps and be kind too yourself,feeling depressed and anxious is normal,but if it becomes completely overwhelming perhaps your GP might be able to help,not all surgerys offer bereavement counselling but mine did and it helped a lot and so did being here.
We are not professional counsellors here but all of us are at some stage of this horrid grief journey so do understand and try to support and help each other along.