You two are naturally similar in energy and temperament, because your birthdays are very close together, even if you were born in different years. Think of the potential between you as your own natural energy, magnified to double-strength. This can work in one of two ways.
Either your connection will flow really well, or all the more trying personality traits that you share will come to the fore, creating problems for the friendship. It's like looking into a mirror -- a very honest one. The truth can hurt sometimes! Especially when it means looking at traits in your own character that are less than stellar. The good news is, your personal rhythms will probably be in sync. However, again, here lies potential for trouble, and it depends on other factors in your charts, not just your Sun signs. Any tendency toward aloofness and independence might make it difficult to maintain a strong connection. But if you both possess natures that ordinarily strive for harmony, you will likely be able to build a strong and devoted friendship.