Unfortunately, yes. Adsense requires all content to be "family safe." Topics such as sexual health or sex tips are not allowed. Even words such as "quickie" and "sexual intercourse" are considered stop words which cause Adsense blank ads to be shown.
If you want to be sure, you can also request a Policy Clarification regarding your site's specific content via Adsense support email.
Personally, I would never use AdSense on a forum of this topic. If you're not moderating the posts, and there ends up being a pattern of stop words that Google doesn't like (however unintentionally) they might decide you're just not worth the risk.
If you're cool with that risk, then keep going. If you're not, then you probably should look into some other form of monetization.