I'm not certain I follow the theory that homosexual relations are idolatry, whereas heterosexual relations outside marriage are apparently not.
Yes, heterosex outside marriage is sin, as is homosex, though the former is due to violation of the type of condition instituted for sexual union by the Creator, that being marriage, while homosex and bestiality are violations of the very manner of union.
The “what of “what therefore God hath joined is male and female,
(Mat 19:4-5) “And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, {5} And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?”
As re idolatry, that is the mother of all sins, and thus is the first of the commandments of God.
Homosexual is rebellion toward what God has ordained (and is usually concomitant with prevalent rebellion in sex and other areas, which foretells the demise of a nation), the prohibition of which, as with all laws, works for our good, and is therefore a manifestation of idolatry, as to whatever has your ultimate allegiance, or affection or trust, is your god, at least at that time. As this is the case, all knowing, willful sin is idolatry, and even in ignorance it is contrary to worship of God in truth.
While even Christians are guilty of idolatry at times, including sadly me (do i always love god more than food, etc.?), which we must repent for, an idolater is one who overall lives for false gods.
In addition to formal false gods, man lives for pleasure, possessions and power/prestige, (1Jn. 2:16) which are false gods which will fails us, but the living and true God is both eternal and almighty, and willing to save that which is lost. To God be the glory, through Jesus Christ.