Hi hardspace, I want to also welcome you to the depression forum. Wow! Iowa...I bet there really isnt much of anything to do there . I can relate to that some what as I live in Missouri and it is boring also, not too much around but cows and farm land but, it is beautiful here. Somehow, someway you have to find and make your own peace with life and the situation your in.
I am sure your parents and sister miss you greatly but, you cant blame yourself for them getting sick or being ill after your absence. Your parents are both old enough to know how to take care of themselves and even though they missed you and went though a depressive stage they should of been taking care of their health. Sometimes, parents have a way of putting suttle guilt on their kids. I'm not saying this is what they did but it kind of sounds like it...Also, whatever problems your sister is having with them because your not there to run interferance between them may be a good thing as perhaps she needs to learn how to deal or form a relationship with them on her own without your help.
It sounds as if your happy with your bf and want to stay with him but your just not too happy or are unsure of the living situation. That is totally understandable. It is difficult to move so far away from everything you know and everyone you love. It would be the same way for him too I'm sure if the situation was reversed? Perhaps like Shy suggested you could go home and visit for a week or so? Or you and your bf can try to look for jobs that are closer to both of your families...like meeting in the middle sort of. Just a suggestion.
I am sure other members will be along to give you some more suggestions regarding this. I hope things get better for you and do please keep us updated and feel free to post away here. Take care