Hi Gravel,
Yes, Adam was there.. you quoted the answer in the text you gave us from Genesis 3. Vs 6 states
" 6 And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat."
There is no doubt that Adam and Eve were together at the time of the fall. Why did Adam not stop her? Maybe because the temptation that attracted Eve to disobey God was one he was also facing every day. It was interesting they were both hovering around the place they shouldn't have been even near too, when the temptation came.
Adam knew the commands from God, and presumably so did Eve, yet both chose to be where they shouldn't have been, listened to and in the end gave into temptation.
Both then made excuses when God asked them why they were hiding from him. 3:12-14, and each received individual punishment for their sins.. both physically ( to the serpant vs 14, to the woman vs 16 and to the man vs 17). Their punishment was emotional (they knew they were naked and they were ashamed vs 7.) It was spiritual (they hid from God vs8-9) and it was geographical (vs 22-24) and it required a saviour to overcome it's effects (Vs 15 is considered the first reference to the messiah in the Old Testament).
Finally, in the new testament, Paul states in Romans 5:12, that sin entered the world through one man.. and death through sin, and in this way death came to all men, because all sinned."
Eve certainly bowed to temptation first.. and it was on the whisper from Satan "did God really say".. but Adam was with her, and he also listened to the voice and he allowed the temptation to be sin. Maybe God held him accountable (and through one man sin entered the world), because God had spoken directly to Adam concerning what he was allowed and not allowed to do in the Garden, but in the end, both received the judgement and the reciprical response from God.. "just as death through one man.. so also God's abundant provision of grace and of the gift of righteousness through the one man, Christ Jesus" ( Romans 5:17).
The bible states sin makes it's entry three ways.. " the cravings of sinful man, the lust of his eyes and the boasing of what he has and does",(pride)
1John 2:16. It was the very temptations that Satan tried on Jesus in the wilderness (Matthew 4). It doesn't surprise me, that the same technique was used on Adam and Eve.. no temptation has seized you than that which is common to man (1 Cor 10:13)
Finally the Bible states that Jesus is the Lamb slain before the foundation of the world .. the fall of man was not an accident. God foreknew it would happen, he gave man free choice and both man (adam) and the woman (eve) deliberately chose to disobey the Word of God and to allow themselves to be in the place of temptation and to allow temptation to become an action that was sin.. disobedience. God knew this was going to happen, and even before the foundation of time, He already had the plan that would bring grace and righteousness to all of Adam's offspring .. the Messiah.