Leaving a wedding early

Hi,

The rule, normally, is that one who eats with others at a communal meal is considered a part of their meal. Therefore, one who eats with enough participants to trigger a mezuman [collective birchat hamazon] is required to stay until a mezuman is performed. At a wedding there is an increased obligation to remain for Sheva Berachot.

One who knows he will need to leave before Sheva Berachot should state explicitly [not necessarily to anyone, though] that he is not participating in the communal meal.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 1:56)

Have a great day,
Mordechai