Can I sue my spouse’s affair partner for adultery in Singapore?

Short answer

No, Singapore doesn't recognise a civil claim against a third party for having an affair with your spouse, sometimes known elsewhere as "alienation of affection." Your legal recourse is limited to your spouse: you can cite adultery as grounds for your own divorce, and the affair may influence how the court views conduct in ancillary matters, but the third party themselves cannot be sued for monetary compensation. However, you can involve the third party in the documents by naming the third party in your divorce papers as "Co-Respondent" in addition to your spouse and serve the divorce papers to both your spouse and the third party.