Short Answer- Yes- it has potential to blow up in your face or at some point shit would hit a fan.
Then again if you two were best friends before you got together, maybe it could work. Did it end amicably, was it mutual? Does she want you back? Do you want her back?
If you move in together, there must be ground rules and lines drawn. If you want to get back with her, I'd suggest not moving in. I ask all these questions so you can be honest with yourself concerning your motives for wanting to ask her to be your roommate.
Why not rekindle the friendship aspect first, work on that and if all goes well perhaps in the future she could be your roomy. For now I'd suggest against living with an ex.
That depends on you though.