Jesus said if He didn't go away the Holy Spirit wouldn't come. He also said He [already] abides with you and will be in you. Is Jesus the Holy Spirit?

Properly, the issue belongs to theology rather than biblical hermeneutics, but perhaps this will be helpful:

Traditional Christianity understands Jesus to be one person (hypostasis in Greek) of the Trinity, while the Holy Spirit is another person. To affirm Jesus as the same person as the Holy Spirit risks stepping over the line into unorthodox teaching. Modalism is one type of teaching that holds that God appears sometimes as the Son but other times as the Father or the Holy Spirit. On the other hand, it is kosher to say that Jesus, the Holy Spirit and the Father all share the same "essence" (ousia).

The OP added that he wants to know if the relationship is like that of Clark Kent and Superman: as long as one is here the other doesn't appear. The answer again is no. Jesus is considered to still be "here" with his followers on earth along with the Holy Spirit. In the Gospel of John, Jesus explains that the gift of the Holy Spirit will be given only after he offers his life as the sacrificial "Lamb of God," not that he himself will appear as the Holy Spirit after he dies.

In John 14:16, Jesus promises “another Helper” (allos paraklētos), meaning someone different from Himself, not Himself again (autos).

In John 14:17, He says the Spirit “stays with you” (pros humas menei) now and “will be in you” (en humin estai) after Pentecost — showing a different kind of presence (see also John 20:22; Acts 2:1-4).

John 14:26 says the Spirit is “sent by the Father in My name” (apesteilen ho Patēr en tō onomati mou), which keeps the Spirit’s mission distinct from Jesus. In John 16:7, Jesus explains He must leave for the Spirit to come (ei mē hypage, ho Paraklētos ouk erchetai), highlighting that the Spirit’s coming depends on Jesus’ going.

Isaiah 11:2 says, “The Spirit of the LORD shall rest (yarum) upon him." This shows continuous, permanent resting, not a temporary visit; the Hebrew verb here implies enduring empowerment.

Similarly, Luke 4:1 says Jesus was “full of the Holy Spirit” (plērēs pneumatos hagiou), this echoes Isaiah; the Greek present participle emphasizes ongoing, active indwelling.

In addition, John 14:9–10 describes how the Father was in the Son and vice versa yet both persons distinct (not Modalism), likewise the Spirit is unified yet distinct from the Son based on the Greek grammar.

For instance, ἄλλος (allos) conveys “another of a different kind or of the same kind but distinct from the one already mentioned.”

Jesus doesn’t roleplay like Clark Kent and Superman; He always remains the same (Hebrews 1:11), where the Greek diamenō means “to continue steadfastly, endure, or remain unchanged,” emphasizing His eternal constancy (Hebrews 13:8).

In other words, Jesus always remains Himself, never changing His identity or adopting different modes. Overall, the Greek shows that Jesus and the Spirit are distinct persons: Jesus is present relationally, the Spirit indwells and teaches believers.

Simply put, the Holy Spirit was indirectly with the disciples through Jesus’ incarnation (Acts 10:38); after Pentecost, the Spirit was directly indwelling them personally (Acts 2).

Answer

Jesus is not the Holy Spirit.

Explanation

It is true that Jesus said if He didn’t go away, the Holy Spirit wouldn’t come.

Why?

It is because the Holy Spirit proceeds from the Father through Christ.

“but to us there is one God, the Father, of whom are all things, and we for Him, and one Lord Jesus Christ, through whom are all things, and we by Him “ (1 Cor 8:6).

But, Jesus is not the Holy Spirit because He talks about the Spirit as distinct from Him.

"for if I do not go away, the Comforter will not come to you. But if I go, I will send Him to you" (John 16:7).

Jesus and Holy Spirit together on Earth

Though the Holy Spirit couldn’t be given during Jesus’ Incarnation, the Spirit given before His Incarnation was very much active on earth when Jesus was here on earth.

For example, when Jesus was a physical baby carried to the Temple, there was a saintly man named Simeon. “the Holy Spirit was on him” (Luke 2:25).

“When Mary and Joseph brought Jesus to the temple to do what the Law of Moses says should be done for a new baby, the Spirit told Simeon to go into the temple” (Luke 2:27; CEV).

There it is, we see both Jesus and the Holy Spirit very much active “together” at the same spot at the same time!

This proves that Jesus Christ is not the Holy Spirit.

The Spirit With

The Holy Spirit can be with anyone; even with evil people!

For instance, the Scripture projects Balaam of the Old Testament as an unrighteous man (2 Pet 2:15).

Yet the Scripture says that the Holy Spirit was on him:

“And Balaam lifted up his eyes and saw Israel camping, by its tribes. And the Spirit of God was on him (Num 24:2).

The Spirit can be on even non-animate things!

“and darkness on the face of the deep, and the Spirit of God moving gently on the face of the waters” (Gen 1:2).

The Spirit `In’

However, the Holy Spirit is given in a person who is called by God to be His child.

“the love of God has been poured out in our hearts through the Holy Spirit given to us” (Rom 5:5).

“When you believed in the Messiah, you were sealed with the promised Holy Spirit, who is the guarantee of our inheritance” (Eph 1:13-14).

“who has placed his seal on us and has given us the Spirit in our hearts as a down payment” (2 Cor 1:22).

“Do you not know that you are God's temple and that God's Spirit dwells in you?” (1 Cor 3:16).

Conclusion

Jesus and the Holy Spirit are not the same individual.