It is entirely a heart thing.
This may sound crazy but, I was in love with a girl for a very long time. And the thought of doing anything to ruin what we had, would have broken my heart. I was so madly in love with her that just to get to hang out with her was a blessing and I counted each second as if it was the most precious thing in the world. I was so in love with her that I respected every fiber of her being, heart, soul, mind, and her strength. Our God was the master of my thoughts and in my innocence I had no idea about what it meant to do "other things." Don't get me wrong I knew about the birds and the bees but, that isn't where I'm going with this.
All I knew was that I loved her and as long as she understood that and would go with me wherever I would go, holding my hand, or waiting for me, that was always going to be so much more than I needed. We were like children. We didn't ask what wasn't becoming of us to ask, we didn't want, we didn't seek for ourselves, we just were ...and that is something indescribable.
I'm 25 now. We didn't wind up working out in the end but, love has a way of allowing us to feel life as it was meant to be. I have tried to recapture it through other means but, love is the only thing worth everything.
I don't know how to answer your question but, maybe its because if you are asking how far too far is, I think you are coming at this from the wrong side. There is no measure to your worth and no line that we draw in the sand that can be your judge. Listen to your heart, Pray and always seek the truth, even when it is least beneficial to you. You are worth more than you can ever imagine, just the way you are and if you feel like you have to change yourself for anyone, it is only because they cannot see how much they don't deserve you.
God Bless