ESV - 6 So when the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was to be desired to make one wise, she took of its fruit and ate, and she also gave some to her husband who was with her, and he ate.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
God's instructions to Adam were very clear as listed in Genesis (2:16-17) but not those given to Eve. However God had instructed her too because when she was being questioned by satan whether God really said that she must not eat fruit from any tree in the garden her answer was "We may eat from the trees of the garden but God did say 'You must not eat from the tree that is in the middle of the garden...' (Genesis 3:2)". She was very clear. She did not say that God asked Adam not to eat. She used the 'plural' form of the first person - we. In addition, when questioned by God afterwards why she ate the fruit she did not say "I did not know or You did not tell me" which would have been a lie in the light of her answer to satan in any case. Instead she, like Adam, tried to blame others, Eve in the case of Adam and satan in the case of Eve (Genesis 3: 12-13). Adam's reply also implies that he knew where the fruit came from because he only blamed Eve for giving him it to him.
There is also an earlier reference in the Bible that refers to God instructing them both (Genesis 1:27-30) before it describes the specific sequence in which each of them was created. So both of the knew that they were not to eat the forbidden fruit for sure.
I would like to return to this question. The question wants to know whether Adam was with Eve. Why? What difference does it make whether he was there or not as they both knew what they were not supposed to do. It was the only thing God asked them not to do.
Unfortunately, this question is not about the sin committed by both but who is to be blamed. These kind of pressures come from today's world where we are preoccupied with sex, gender, PC, equality and many other issues. I have read many discussions in religious texts and have listened to many who have used this story to blame Eve, a woman, for eating the forbidden food first and then for giving it to the man making the latter the innocent victim of the former. In effect according to them the woman is to blame and that is the reason why men are superior, why men are selected to hold leadership positions, why women are not fit to do what has been assigned for men to do in the Church etc. In fact if that is so then ask yourselves why didn't Adam instruct or prevent Eve from eating the fruit in the first place and why he didn't refuse it when it was offered to him by Eve? The point is that Adam's actions show that he was a terrible leader (only one other person to lead) and a very bad role model for anyone to follow. So don't listen to anyone who tries to use this or other Bible stories to justify why we men were chosen by God to lead. In fact the moral of this story is simple - "Whether we are men or women, we must not disobey God's instructions and not be tempted by satan. Anyone who is fit to lead should be able to do so. Instead we should work together collectively to help and lead our fellow humans to find God by our actions".
It is clear that Eve ate of the forbidden fruit first. Wherever Adam was he must have seen Eve go into a in a state of spiritual darkness and therefore separated from God and himself. Adam must then have realized that as Eve had fallen into this sinful state, unless he, himself, followed her, there would be no chance what-so-ever of salvation. So Adam willfully ate of the fruit so that he could join in what Eve had done, in the knowledge that God would find a way of saving them both. Adam also must have been aware that he was the father of the human race as a whole and therefore it was his duty to follow Eve into sin in order to save not only himself but also the whole human race. Jesus refers to himself as the second Adam. He also made a willful decision to go to the Cross, take away sin, and put to death the Adamic sinful nature.