:This Adama thing is kind of explained in the scene by the photo wall, where he sees her picture and kinda goes "I can't leave her behind after all we went through". Decision of the heart, blah blah blah... 
 :Hera's real importance is only revealed in the last scene, where she turns out to be the mitochondrial Eve from which our entire race descended. Of course the Old Man would never know that, but maybe some "angel" whispered it into his ear. (God, I hated this angels crap...)