All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
Allah says (what means): {And among the people are those who take other than Allah as equals [to Him]. They love them as they love Allah. But those who believe are stronger in love for Allah.} [Quran 2:165]
Two meanings were reported regarding the part that says {…they love them as they love Allah.}
The first meaning is that the polytheists love the idols which they worship in the same manner that they love Allah, so they have equal love for Allah and for those false gods. In other words, those polytheists love Allah, but they love whatever they worship as well in the same manner in which they love Allah. Then Allah clarified that the believers are stronger in love for Allah than the love of the polytheists for their idols.
The second meaning is that it means that the polytheists love their idols in the same manner that the believers love Allah.
The first meaning is the meaning favored by Shaykh Ibn Taymiyyah and his student Ibn Al-Qayyim .
Ibn Al-Qayyim said:
“Shaykh Ibn Taymiyyah favored the first view, and said, ‘They were rebuked because they associated between Allah and their equals in love, and they did not purely love Allah as the believers loved Allah. This equality that is stated in the saying of Allah is a narration from them while they are in Hellfire, saying to their gods and equals who are present with them in punishment: {By Allah, we were indeed in manifest error. When we equated you with the Lord of the worlds.} [Quran 26:97-98] It is known that they did not make them equal to Allah in Creation and Lordship. Rather, they equaled them to Allah in love and glorification. This is also the equality that is mentioned in the saying of Allah (which means): {Then those who disbelieve equate [others] with their Lord.} [Quran 6:1] That is to say that they equate others with Allah in worship, which is love and glorification. This is the more correct opinion of the two.’”
Such polytheistic love is the love that involves full humiliation and exaltation in the heart of the person; exalting the beloved one and glorifying him in a way that entails complying with his orders, refraining from his prohibitions, and equaling him with Allah in these matters or favoring him over Allah in them. So this love is worship and is a polytheistic act; hence, whoever loves anyone other than Allah with a love of worship is a Mushrik (i.e. he is committing an act of Shirk; associating partners with Allah).
A man loving a woman [who is not his wife] just out of lust is like all other kinds of love that are included in the totality of sins and do not escalate to major Shirk; however, he is in great danger, especially if the matter reaches Zina (fornication or adultery), because Zina is one of the grave major sins and one of the most heinous sins.
The Prophet negated faith from a person who commits Zina, as he said, “No adulterer (or fornicator) is a believer at the moment when he is committing adultery.” [Al-Bukhaari and Muslim] It means that he does not commit this sin while he has full faith; these are among the wordings which are said to deny something, and the meaning is to deny its perfection.
The Prophet also said, "If a man commits Zina, faith comes out of him and hovers over his head like a cloud, then when he stops (this act), faith returns to him." [At-Tirmithi - Al-Albaani graded it saheeh (sound)]
Therefore, a fornicator or adulterer is obliged to repent to Allah; the same goes for any man who had an affair with a non-Mahram (marriageable) woman, even if he did not commit Zina with her; and one should not find excuses in the sense that his sin does not escalate to the extent of polytheistic love.
Allah knows best.