In ancient times, a member of the wedding party was known as the shushbin. We find that when Samson (=Shimshon) was married, he took thirty young men to be the close members of his wedding party. In Talmudic times, the wedding feast was often made as a communal meal and the attendees were called the shushbinim (plural of shushbin).
In modern times, we often have more than thirty guests at a wedding. The shushbinim in our days are not the only attendees but the closest friends (the members of his "do-re" in Persian culture) of the groom. The bride also has her shushbinim (or bridesmaids). One of the shushbinim -writes Rabbi Aryeh Kaplan- would be at the groom's or the bride right hand, and take care of all his or her needs. It could be a friend or a relative of the groom (a brother, a cousin, etc.) He would act as the groom's secretary and valet, seeing the details of the wedding. He would often announce the honors at the ceremony and would make sure that the ceremony and dinner run smoothly. In modern terms, we would call this shushbin "the best man".
Maimonides dedicates a whole chapter in Mshne Tora (zekhia umatana, chapter 7) to describe the function of the shushbinim, which is radically different from the modern concept of the best man (or "men"). He says that the tradition in all Jewish communities is that when one gets married his close friends give him some monetary gift to afford the expenses of the wedding. These close friends, whom with their gifts assist the groom to afford the wedding party, are known as the shushbinim. In general, Maimonides explains, the monetary gifts are given generously, of an amount above the cost of the food the friends are served at the party. In return, the groom is expected (read: legally expected) to do the same thing toward his friends when they get married. Thus, everyone in that group of friends supports each other to afford the expenses of the wedding party.
Read LOVE INFUSIONS "Three ways to bring love back into your relationship". By Rabbi Shlomo Slatkin, from Aish.com