Mostly we operate from a presumptuous mode. We never stop to ask if the other person feels for us the same way we feel for them. Until that moment when you need a hand, a shoulder, a friend and the other person gives you their back we presume we are operating on the same wave length. I suppose what makes it hard is that we don't court friends the same way we do partners. With someone you end up dating you state your purpose but with friendships we presume all those that smile at us feel the same way we do.
The pain is devastating especially because the signals we thought we read right may not have been signals at all. Maybe that person was looking for a fling