Deckerstar sounds better. It's just a mix of their names.
Apparantly a common way to address a specific relationship is to rape the names of the participants and mash them together, in this case creating an ill-advised love child of the surnames "Decker" and "Morningstar".
In case I didn't make it clear, I'm not a fan of this practice. But if you can't help yourself and feel the pathological need to do something so horrific, please do it right and create something that doesn't sound like a vomiting giraffe. Like Clucifer.