Sexual MISCONDUCT is an akusala kamma. That could make one eligible to be born in the apayas.
But having sex is not an akusala kamma. Sex becomes an akusala kamma if it is harmful to the other person(s), i.e., if it is a child, someone else’s partner, etc.
Is It Necessary for a Buddhist to Eliminate Sensual Desires?
One can have cravings for sex or any other “legitimate” sense pleasures and still can become a Sotapanna.
– One needs to abstain from sex (or any other sense pleasure) to attain the Anagami stage: