Notice that, though described as a woman, she is in reality a nation that other nations admire. Israel's marriage to God bound her to keep His laws (Exodus 19:8), but she was not faithful. Harlotry entered the relationship. From this point on in the relationship, her harlotry—the fornication and adultery of the woman—is either implied or directly stated in virtually every remaining verse in Ezekiel 16.
The liberal Interpreter's Bible Commentary says that Israel is portrayed as a wife who became a pagan temple-prostitute. That is a possibility, but the conservative commentaries seem to be more correct. She is portrayed as an unfaithful wife whose faithlessness is displayed in a far wider range of activities than just worship. Israel, the nation and wife, is unfaithful in every area and activity of life in which a faithful wife/nation would normally be involved.
Her sins are described in sexual terms because sexual sins are the most common way infidelity in marriage is shown to the public. Everybody can relate to it. Despite the commands of her Husband, Israel simply did whatever she wanted to do, when she wanted to do it, and how she wanted to do it. Amidst the business of daily life, she simply ignored or completely forgot the vows of faithfulness given in former years to God.
The harlotry implied is clearly the breaking of the terms of the marriage covenant. Her harlotry is unfaithfulness, disloyalty, and is primarily spiritual in nature. The most ruinous spiritual sin behind these sexual terms is gross idolatry, but all other sins are included. Israel was unfaithful in managing God's green earth and in conducting business both domestically and internationally. She revealed her infidelity in the wreckage of millions of her citizen's marriages and child-training practices. She showed herself faithless when her people lied to, stole from, lusted after, and murdered each other. She proved herself to be disloyal and ungrateful by forgetting from whom came her great blessings and worshipping things made rather than the Creator who made them.