Is he/she having an affair?

Asking this question assumes that the parties involved have made some sort of overt monogamous commitment to each other, otherwise they are free to do as they wish and seeing someone else cannot be constituted as an affair. Although this may seem too obvious to state, many people make the mistake of assuming a commitment to exist where it does not and create great heartache for themselves simply out of a failure to clarify the rules of relationship with the partner. If something you are concerned about has not been discussed outright, do that first and establish agreement where before there was merely assumption. Granting that the rules between you are clear and you suspect a partner of violating your trust through involvement with someone else, it is generally wise to seek counsel first with someone you trust who can give you level-headed feedback and help you come to clarity in your own mind about the truth of the situation. If you do not know anyone like that then a professional counselor or astrologer can be of great assistance. And if you remain convinced of the affair, confront your partner with the concern and the evidence for the concern at a time when the two of you can have two to three hours alone to discuss the manner. Do so in a respectful manner that allows both of you your full say and the freedom to respond with emotional honesty. If there are children involved, have a trusted friend, family member, or neighbor watch them for you during the time it takes for the discussion.

Remember: If there is any possibility that your partner may respond to the confrontation with violence, consider your safety first and seek professional counseling before taking any action! There are clearly other issues to be resolved before the matter of a possible affair. This is never an easy issue to face but if done rightly it can potentially bring to surface trouble spots in the relationship that, when faced guidance and love, can ultimately lead to healing.