If the holy Spirit comes from God the Father, how can Jesus say this? It is through the doctrine of the Holy Trinity that Christians, and Trinitarians specifically, state that the Three Persons are One God. Since the Three are One, Jesus can do this, and therefore, Spirit can proceed from both the Father and the Son. Saying the Spirit proceeds from the Father is correct, but also saying that it proceeds from the Father and the Son is also correct.
The Holy Fathers at Constantinople in 381, completing the Creed begun at Nicaea in 325, thought it right to speak of the Spirit proceeding from the Father (alone), even as Our Lord did. The Holy Fathers at Ephesus declared the Creed unchangable.
You cite a temporal event: the Gift of the Spirit to the Apostles in time. The filioque confounds the temporal mission of the Spirit, which is through the Son (as St. Maximus the Confessor observed, striving in charity to find an Orthodox reading for the western innovation), with the Eternal Procession, which is from the Father. This confusion of the temporal and eternal, of the Uncreated with the created (or the relationship of the Uncreated and created) is the root of all Western departures from the Orthodox Faith (including created grace, of which purgatory is the most well-known example, and the false papal ecclesiology).
I pray that you will get the chance to debate your interpretation of Scripture with the Harps of the Spirit in the Kingdom. For my own part, I will reply, as St. Aleksander Nevsky did to the Crusaders, "The Traditions of the Seven Councils we scrupulously keep."