We will have been married a year on June 25th.的been是什么

marry,结婚不是延续性的动词,是瞬间的。
He is going to marry her。他要娶她。

married 结了婚了的。形容词,这样才能表示延续性的结婚的状态。所以会有be married。He is married。他结婚了的。

原句可以这么看

We are married。我们结婚了。

要表示结了1年,在6/25的时候
We have been married for a year on June 25

但6/25是将来的时候
We will have been married for a year on June 25。