Firstly, I am sorry for your loss. I truly understand how you feel.
I am an only child; lost both of my parents (with whom I was EXTREMELY close to both) to cancer within 2.5 year of each other. I really have no family I keep in touch with; I have an out of state uncle and his wife and that's pretty much it.
It hurts deeply that I've been out of state to see this only blood relative with whom I thought I was close; however, for the past year he's been promising they would come visit (we only live about 4 hours from each other) but keeps blowing it off.
I guess the only way I'm dealing with it is pretty much writing them off in the way of having any expectations for the relationship to be as I wish it would be. I have gotten myself to accept the way it is; all the "if you need anything please call us" are just lip service, as they knew my personal situation was in an upheaval, especially when I lost my dad earlier this year, and never ONCE did they offer to come up and spend time with me.
We can't force people to act as we think they should so I think being realistic about it is the best way to handle it. Sad it has to be that way.