Originally Posted by Great Mind(s)
See to me, they didn't even have a relationship. It was a tease for both characters and Mystique chose Magneto. I think it would be silly to have her go back to Beast especially when the idea of Azazel + Nightcrawler's origin could be explored...
They obviously both cared for each other. It wouldn't be hard to imagine Beast trying to "save her" from Magneto and the Brotherhood.