The answer has a lot to do with how you define what exactly a relationship is. I have always held a view of relationships as a threesome - me, you and our relationship. We each bring something to the relationship. I take care of myself, you take care of yourself, and that leaves us in a position of strength from which we can contribute to a relationship. I contribute at a level I am comfortable with, you do the same.
Healthy people build healthy relationships.
It's possible that one person may come to feel that he or she contributes more to the relationship than the other person, so much so that a sense of unfairness develops. In these cases we either have to learn to expect less from the relationship, cut back on our contribution to the relationship, or end the relationship. But we are always free to contribute to the relationship at a level at which we feel comfortable. That level is our own to set for ourselves. For me, the question of telling my friends has always come down to motives.