Ye shall not go in to them, i.e. marry them. See Poole on "Genesis 6:4". They will turn away your heart after their gods: possibly Solomon might think himself too wise to be drawn to idolatry by his wives, and therefore to be unconcerned in the reason of the law; and consequently free in some measure from the obligation of the law; and so, like our first parents, trusting his own fancy more than God's word, he fell dreadfully.
Related Commentaries of 1 Kings 11:2
1 Kings 11:2
2 Of the nations concerning which the LORD said unto the children of Israel, Ye shall not go in to them, neither shall they come in unto you: for surely they will turn away your heart after their gods: Solomon clave unto these in love.