To answer the questions, we must first review the concepts of spiritual death and spiritual life.
According to the New Testament, all human beings on earth today are the biological descendants of Adam (Mark 10:6 and Acts 17:26). At the time when Adam sinned, God cursed the ground, and this cursing of the ground consigned Adam and his descendants to "return to the dust" (Gen 3:19).
Romans 5:22 (NASB)
22 Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned—
When sin entered the world through Adam, physical death resulted. For example, one of the sons of Adam, Cain, murdered his brother, Abel. This incident was the first recorded instance of human death. Adam and his biological descendants therefore not only experience physical death, but they also lean toward destructive behaviors such as appeared in Cain against his brother Abel. In other words, the sin of Adam resulted not only in visible physical death, but invisible spiritual death as well.
Spiritual death is not explicit in the Hebrew Bible (Old Testament), but is more apparent in the Christian New Testament. There are at least two places in the New Testament that imply that spiritual death occurred when Adam sinned in the Garden of Eden.
Eph 2:4-6 (NASB)
4 But God, being rich in mercy, because of His great love with which He loved us, 5 even when we were dead in our transgressions, made us alive together with Christ (by grace you have been saved), 6 and raised us up with Him, and seated us with Him in the heavenly places in Christ Jesus,
Col 2:13-14 (NASB)
13 When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions, 14 having canceled out the certificate of debt consisting of decrees against us, which was hostile to us; and He has taken it out of the way, having nailed it to the cross.
The phrase "made us alive" is the free gift of eternal life (John 3:16), and therefore what is implied in these verses cited above is that human beings are born without eternal life, and in this respect they are born spiritually dead. For example, when Adam sinned in the Garden of Eden, God removed access to the Tree of Life from Adam in order to preclude Adam from indefinite mortal existence.
Gen 3:22-24 (NASB)
22 Then the Lord God said, “Behold, the man has become like one of Us, knowing good and evil; and now, he might stretch out his hand, and take also from the tree of life, and eat, and live forever”— 23 therefore the Lord God sent him out from the garden of Eden, to cultivate the ground from which he was taken. 24 So He drove the man out; and at the east of the garden of Eden He stationed the cherubim and the flaming sword which turned every direction to guard the way to the tree of life.
When viewed through the lens of the New Testament, this passage in the Book of Genesis suggests that Adam had suffered spiritual death when he sinned in the Garden of Eden. So in these respects, Adam and Eve brought spiritual and physical death into the world.
So, to answer the question of the OP, the believer in Jesus Christ receives eternal life, and so ontological spiritual death is converted into ontological spiritual life at the point of faith in Christ Jesus. (The New Testament seems to indicate that believers receive and share the eternal life of Christ Jesus because of union with him.) But since believers still possess bodies that are the biological descendants of Adam, they still are subject to the curse of the ground, which beckons them not only to inevitable physical death, but also to destructive tendencies as was apparent in Cain who murdered Abel. So the idea in Gal 2:20, which is the topic of this posting, is that the body of the believer (which is subject to the curse of the ground because of Adam) had died on the cross with Christ Jesus, and so this sinful power of Adam had died. That is, the believer is made one in Christ Jesus (the new Adam), so that his death on the cross and his resurrection apply in equal measure to the believer. That is, the reckoning of our bodies in the death of Christ Jesus on the cross crucifies the destructive tendencies of our Adamic bodies (Gal 2:20 and Gal 5:24), and this reckoning must occur on a daily basis (Rom 12:1-2).
Because of this "joint-crucifixion" in union with Christ Jesus, the believer is therefore no longer consigned to the power of destructive proclivities and tendencies stemming from Adam. Because of this "joint-resurrection" in union with Christ Jesus, the believer received immediate eternal life and will also one day receive the glorified body because of union in the resurrection of Christ Jesus, whose eternal life is more powerful than death (Acts 2:24).