Well we know that the command not to eat was given to Adam....and the freedom to eat all but. Eve on the other hand was deceived, and we know sin came thru Adam's direct disobediance to God's command.
I don't know why God didn't reveal what was Adam doing the whole time the conversation between Eve and Satan was occurring...but we know she simply 'turned' and gave it to Adam and he ate... without resistance apparently. So he likely was there as this conversation took place.
But I don't see any indication he attempted to save Eve in what's recorded.....it's a mystery I am anxious to ask the Lord about when I see Him. Why didn't Adam stop it? Why did he yield?
My point is that it was recorded, in the actions of Christ as the 2nd Adam. The actions of the 2nd Adam point back and help explain the actions of the 1st Adam. Therefore, the 1st Adam willfully 'became sinful' out of love for his fallen bride, just as the 2nd Adam 'became sin' out of love for His fallen bride.