楼上别乱说：have been是现在完成时态。表示已经做完，以后不做。另一个是will be将来时态。楼主是要表达一种客观真理，一种状态。应该这么说：i am with you and i will always be with you。这样同时表达了状态和将来的会发生的状态。
I'll be with you.
I've always been with you.
I accompany you.
