How to Know if Your Girlfriend/Boyfriend is Cheating on You

1. 1
   Look back at your relationship. Have things changed recently?
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   Watch out if your partner is suddenly going out. Act laid back and pretend not to suspect anything. The next day or morning try to act a bit romantic; don't say anything about another person you might suspect. You want your partner to have a bad conscience if he or she is doing something stupid.
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   Take note if the person you're with is acting weird.If they suddenly jealous of everything and everyone, something is definitely going on. (This is mostly referred to men but remember everyone’s different.)
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   Take note if your partner suggests that you are cheating on him/her and you are not. It could mean he/she is. There's always a possibility this might just be jealousy. If you aren't interacting with the opposite sex more than usual, however, jealousy is not the case.
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   Find out for sure. You need information; you can't just jump to conclusions. Of course numbers and dates on pieces of paper are proof, but they’re not enough. Try sneaking in questions that might not seem suspicious into your everyday conversations, but that will give you a name or info you might not have been aware of. Do this when you believe your partner has let their guard down.
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   Know that you are at risk. Remember that accusing someone of cheating is serious business. You might end up breaking up with a really sincere person.
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   Let them go if he/she confesses to have been cheating. It’s not good to go out with a person who cheats. How you deal with that person after finding out is your own business. The most important thing to remember is not to forgive that person for their serious error. If you weren’t enough this time you’ll never be. But don’t try to make that person jealous that’s the same thing as lowering yourself to that person’s level.
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   Keep in mind that you may see it with your own eyes. The only positive thing here is that you now are definitely sure about the situation. If so you should handle the situation directly. Do not run away for any reasons. Look the person straight in the eyes, but don’t lose your temper or start fighting. Then leave or if it’s your place, throw them out in a manner of speech.
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   Do not ever go back to a cheater. As well, do not to connect yourself to a former cheater. This will only make your life difficult. Once a cheater always a cheater! Although, this isn't always the case; some people can realize that cheating on a nice guy/girl is wrong and say they'll never do it again and be sincere when they say it! Don't make harsh decisions.

Source: www.wikihow.com