I used to not be able to sleep alone... Then my husband started working nights and I had to get over it. It was hard, I went weeks without sleeping more than a few hours each night, but eventually I got over it and now have a fairly normal schedule. It is possible to adapt to new situations and when a relationship structure changes from including 2 people to including 3, it calls for some pretty big adjustments.
My husband having a commitment to work is no less important than your boyfriend and girlfriend having a commitment to you and your relationship. It should be a priority for them to learn how to adapt their habits in a way that allows them to share their lives with you. And I very much agree with sparklepop and nycindie that it sounds like your girlfriend needs to get over herself, grow up a bit, and recognize that other people have feelings and needs too.