Here is the issue, MamaZ, the NASB renders John 14:16 as: "And I will ask the Father, and He will give you another Helper, that He may be with you forever." But the ESV renders it this way: "And I will ask the Father, and he will give you another Helper, to be with you forever." And if you look at other well respected translations, you find they are split 50/50, with YLT, the NKJV, and the NASB using "may be with you," but the NIV, ESV, and HCSB using "will be with you." So I am unsure if the grammar is decisive, or whether the translators chose their version without a basis from Greek grammar. The NIV often strays off the grammatical center, but not the NASB, YLT, HCSB or ESV.
Here is what an Online Interlinear says: the Greek word transliterated as "eimi" is in this form: eimi
vs Pres vxx 3 Sg
it-MAY-BE
he-may-be
Because the mood is subjunctive, "may be" rather than "will be" might be indicated. Do you know? And further, if the circumstance in view is a possibility, rather than a certainty, is the circumstance whether God will send the Helper in response to Christ's request, or in other words, is Christ choice of words asking rather than telling, i.e not assuming that the Father will send the Helper, or is the circumstance in view whether or not the Helper will stay forever. I believe the former view is the idea and therefore "will be with you forever" is the best translation.