Do you think it is possible to have a sexual relationship with an ex? If so how would you ask or bring this topic up? I am thinking about her sexually often

I think anything is possible, however, best to be prepared and informed before you jump the gun. First, are you both single? If so, this makes it much simpler. If not, I would strongly advise not to attempt a rekindling of this kind. I would ask in an open & honest conversation face to face. Talk about how you feel about your ex & what you would like to happen between you. If you move forward, be cautious of one thing. Becoming a couple all over again. This is more than likely going to happen as sex is difficult to have without developing feelings for one another. In all cases, you can never have your cake & eat it too. Especially if you have had strong feelings for this person in the past. Might be easier and less painful to just let go of this idea/person and move on. Become one with yourself and eventually develop a relationship with a new partner. Let me know how it goes!