Open and honest communication is the best chance to avoid inevitable disaster. It may still happen, but you have the best chances of it not.

I would sit down with Jane and tell her that if you have seemed distant it is because you have feelings for someone else and that the spark isn't there. If you wish to end it, you will need to because otherwise you are just going to drag her along.

It also sounds like you really need to talk to Emily and find out if she will reciprocate or if you need to move on. Maybe Jane could be someone of interest but you can't see it because you are infatuated with Emily. Or even if not Jane who else are you missing that could be amazing just because you saw Emily first?