I don't see emotional pain as a plus in making you a stronger person. Emotional pain tends to wear a person down, and unfortunately builds-up painful defenses. As time goes by though, we learn to avoid that which hurts us as much as we can. Sometimes to our detriment.
I don't know that it makes you stronger but maybe better able to cope with difficult and painful things that happen as a part of life. You learn that you are greater than the hurt and can move past it to better times and happier things.