I think people are using the word 'right' in a more colloquial sense. In the strict sense of the word-- as something to which one is entitled by virtue of the natural or supernatural law-- I find it very difficult to assert that someone is entitled to know the sɛҳuąƖ history of a non-spouse. I think what people are more saying is that whether or not a spouse is a virgin or a chronic masturbator is going to factor into their evaluation of the spouse's fitness, and hence, is something they would like to know and have reason to know. And yet, I think in most cases it would not really be a right to know.
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Rights and duties correspond, so if one person has a proper right to a certain piece of information it means another has a proper duty to provide it. Is it the case that fornicators and the like, especially when they are repentant, are duty bound to disclose their past to others? At what point? Is it first date kind of stuff? Engagement kind of stuff? At what point has the fornicator morally sinned in failing to disclose? This seems like Scarlet letter type stuff.
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Here's where it could become a right. Suppose a virgin suitor says they would never marry a non-virgin. At that point, their consent to marry enters into the picture, and the non-virgin suitor would seem to indeed have a proper duty to disclose, probably out of charity and to prevent them from consenting to something that they would not otherwise consent to.
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All that said, it seems that in general, prudence suggests disclosing for a few reasons, even if there is no proper duty/right to give or receive the disclosure. There is a good chance such information will be revealed later anyways: social media being what it is, people's histories being shamelessly advertised, etc., suggest that a non-virgin spouse will eventually be found out. Better to disclose it at some point in the courtship than for it to come out later, and possibly risk the other spouse feeling betrayed. For men disclosing pornography use to their girlfriend's, same idea. Especially if the use has been 'addictive', because it is unlikely, in a digital world, that such a secret will be able to be maintained forever. None of this constitutes a duty/right, I do not think, but something can be the best thing to do without there actually being a duty to do it.
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It being a question of prudence (i.e., good moral/situational judgment), there will be cases where it is prudent to not disclose, too.