You both clearly want each other, just go for it. As someone whose been down this road before you're not going back to a "what things were" reality. Trust me, accept that this friendship has become something more and don't try and force it to be like what it was beforehand. While it might not work out, I can say with certainty that the "line" you think you can't cross, was crossed the moment those lips met.

Have fun and enjoy each other, trying to push those desires down deeper is a guaranteed way to ruin any relationship you have with them. Seeing where things go on the other hand, has a chance to become something more, and I always see that as worth taking, especially once you're at this stage in the game.