Jesus was always fully God and fully man. He existed with God the Father since before time and entered His own creation. He took on flesh to live out the law as the perfect Adam and fulfill it. "Father, why have you forsaken me." was when He became the sacrifice and took on all the sins of the elect then and in the future and He experienced the separation from God the Father for the first time that we as sinners have as our nonmail state. Every time you sin you are adding to contributing to what Jesus suffered on the cross. But once you die or Jesus returns in final judgment you will be in perfect harmony with the Father as Jesus was and is once again without sin separating you from His Holiness.

This is clear in any Christian confession and Catechism as well as scripture.

Adam took something OFF a tree and sin entered the world and it decayed. Jesus, the perfect Adam, was out ON a tree (the dross) and the Gospel entered the world and it is slowly growing and spreading like levin in the dough until the world is restored to the garden.