A) Honestly?You should come clean with your friend & ask her if she has a problem with you being interested and/or dating her ex.If she does....then the two of you could work it out,hopefully for the better.If she doen't then it's all good.Either way you wouldn't be hiding it from her & she could very well respect you more for the fact that you were a stand-up person & told her.
Q) Is it possible to love two people at the same time?