This is a really tricky one. You must be sure that your apparently strong feelings are not the result of a crisis within your own relationship. The rosy glow of an imaginary relationship can look far more attractive that an exisitng one with problems, but that doesn't mean that this is a viable future for you. Confirming your feelings is a step forward from which you cannot step back, so you need to be very sure indeed of your future before you embark on any life-chaning decisions. If in any doubt at all, do nothing. You need to put your energies into your current relationship and ensure that it is beyond redemtion. Then you can be sure you are not losing anything by exploring a possible future relationship with your girlfriend's friend. You need to be sure that your feelings really are returned, not just because you'd like them to be. This needs careful thought, and plenty of it before you do anything that may wreck everyone's relationships. Good luck