Any ways to subtly tell if someones cheating?

[Monica]

Without him or her knowing

[Alexis]

If someone is cheating they usually because very protective over the person they are cheating on. Example; Your boyfriend is cheating on you he may
-start to accuse you of cheating
-Be all over you (Your facebook,Twitter,cell phone, etc)
- They usually become very bipolar
* One second they are mad at you for talking to a guy, The next he's so sorry and cooking you dinner.)
-You tell him "I need to talk to you." and he starts to question you why and gets nervous.
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If you're asking how to cheat without him or her knowing... My answer is don't. It's never a good idea. If youre going to chat on someone you may as well just break it off with them .