With whom does Jesus have fellowship during his time on earth?
Your first thought might be the disciples. But think about the way he relates to them, or rather the way they relate to him. It's all a little strained, isn't it? They do not understand him, do not 'get' his mission, do not grasp his identity. Read through the gospel accounts of Jesus' life - even when he is surrounded by a crowd, you can't shift the impression that Jesus is alone. He stands apart, even from those whom he has called to be closest to him. He is with us, but not really one of us. In fact, it is only when Jesus is alone that we see him in fellowship - with God his Father, in prayer. One of the most intimate moments is in fact the agony of Gethsemane. The Father is with him; the disciples are sleeping.
Fast-forward to Calvary. Consider Jesus on the cross. With whom does he have fellowship now? I think it is clear that just at this point Jesus has fellowship with the criminals. He is with them, and they are with him. Through them, he claims fellowship with sinful humanity generally. He is with us, as one of us, in our condition. It is not coincidence that just at this point he can no longer claim fellowship with the Father - "My God, my God, why have you forsaken me?"
The resurrection proves that that loss of fellowship was temporary. He was vindicated by the Spirit, received back into full enjoyment of the fellowship of the Trinity. Did that mean, then, that his fellowship with us, wretched sinners that we are, would be broken? Would there be a parallel movement to the change we saw at the cross?
No. He was delivered up for our sins, but raised for our justification. His fellowship - solidarity, kinship - with us is just as solid as when he died our death on the cross; but now with him we enjoy fellowship with the Father. In him, we are accepted.