Even if you regret something, it is selfish to keep the truth of your actions secret from your partner who you should respect by serving them with honesty. Forming a relationship on a basis of lies due to reservations about your past mistakes is unfair to both parties involved.

Although virginity might not be a "big deal" to one, it could be a huge thing for another which should be considered when falling down this slippery slope of distrust. Not to mention if she trusts him to be a "virgin" she could fall at risk to any number of mysterious STDs from the decision to not use protection based on false pretenses.

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In a healthy relationship, especially long-term, one's feelings should not trump the others. It's immature to fail to consider the consequences that lying to your counterpart about anything, big or small, poses to their psyche moving forward.