Mixed emotions and afraid of losing her.

I separated from my ex two years ago and since then have developed a very strong bond with my stepdaughter. She treats me as if I am her father and loves me as such. There is a very deep love between her and I and I am always there for her, while her mom remains somewhat emotionally distant by nature. No hard feelings, Its just her way of doing things so I stepped up to fill the gap. But, because I have no legal rights at all and am not really entitled to any,I struggle constantly with mixed emotions and a terrible fear that her mom might just one day pull the rug out from under us or manipulate her into cutting me out of the picture for petty or unfounded reasons. This would devastate me … and hurt my daughter in a huge way, because no one really understands just how close we are and how much she relies on me for emotional support. My daughter hides nothing from me and has told me some very serious secrets about her life that I have not shared with anyone. She needs me more than anyone realizes. The fact that shes 16 and going thru all of the stuff that comes at that age just makes it even more difficult. I feel like I am walking a tightrope all of the time. With no safety net at all.