Homosexual “sex” acts are a sin.
You don’t need to refer to God’s revelation in the Bible to know this.
Natural law and complementarity teaches us that the two ends of the human sexual organs are procreative and unitive, and as such, it is only right to use them in a manner by which these God-designed purposes are fulfilled.
Even atheists will generally assert that there are “wrong” ways to use our bodies, such as overeating or raping others.
Following this line of logic to its natural end confirms the truth: that, like masturbation or sex that does not end in insemination, homosexual “sex” acts (I say this because one man ejaculating into another’s colon is not sex) are clearly wrong, and by extension, homosexuality is near occasion for sin.
Repent!