The difference between how the Holy Spirit and Son "proceed" from the Father

The Nicene Creed states that the Holy Spirit proceeds from the Father: >and [we believe] in the Holy Spirit, the Lord and life-giver, who **proceeds** from the Father. > >καὶ εἰς τὸ Πνεῦμα τὸ Ἅγιον, τὸ Κύριον καὶ Ζωοποιόν, τὸ ἐκ τοῦ Πατρὸς **ἐκπορευόμενον**, The word ἐκπορευόμενον is a participle derived from the Greek verb ἐκπορεύομαι. I'm assuming that the authors of the Nicene Creed derived that statement of faith from John 15:26 which states, >But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which **proceedeth** from the Father, he shall testify of me: (KJV) > >ὅταν δὲ ἔλθῃ ὁ παράκλητος ὃν ἐγὼ πέμψω ὑμῖν παρὰ τοῦ πατρός τὸ πνεῦμα τῆς ἀληθείας ὃ παρὰ τοῦ πατρὸς **ἐκπορεύεται** ἐκεῖνος μαρτυρήσει περὶ ἐμοῦ The point is that the Holy Spirit is said to "proceed" from the Father. Now, concerning the Son, in John 8:42 , it is written, >Jesus said unto them, If God were your Father, ye would love me: for I **proceeded** forth and came from God; neither came I of myself, but he sent me. (KJV) > >εἶπεν οὖν αὐτοῖς ὁ Ἰησοῦς εἰ ὁ θεὸς πατὴρ ὑμῶν ἦν ἠγαπᾶτε ἂν ἐμέ ἐγὼ γὰρ ἐκ τοῦ θεοῦ **ἐξῆλθον** καὶ ἥκω οὐδὲ γὰρ ἀπ᾽ ἐμαυτοῦ ἐλήλυθα ἀλλ᾽ ἐκεῖνός με ἀπέστειλεν There, the author uses a conjugation of the Greek verb ἐξέρχομαι. 1. What is the difference between the manner in which the Holy Spirit proceeds from the Father and the manner in which the Son proceeds from the Father, between ἐκπορεύομαι and ἐξέρχομαι, respectively? 2. Why is it commonly confessed (e.g., in the Nicene Creed) that the Holy Spirit, but not the Son, "proceeds" from the Father? (There's also at least one verse, totally unrelated context, mind you, that features both verbs: Matt. 15:18 .)