Signs

Reference: http://www.wikihow.com/Know-if-Your-Girlfriend-Is-Cheating-on-You

Watch for potential signs.

• Secret phone conversations: Does your partner leave the room every time they get a call on their cell? Are they just trying to be polite? If your partner is trying to guard their conversations on the phone, there may be reasons to worry.
• Distinct changes in appearances: If your partner suddenly starts worrying a little more about their appearance, (new cloths, always clean shaven, spending more time in the mirror) they may be trying to look good for someone else. If they get dressed up for you, that's one thing but if they seem to spend a little more time looking good to go out without you, you might want to look into that.
• Picking fights: Is your partner picking fights and arguing more with you? This could just be an excuse to get out of the house. Picking a fight and then storming out of the house to get away from you is an easy way to go spend time with someone else.
• Lying: Catching your partner in a lie no matter how small is always cause for concern. Try to connect lies with certain time frames and you may have a connection to infidelity.
• Computer time: An increase in computer time may be one of the 7 signs you are being cheated on. There are many adult chat rooms out there that cater to infidelity. Check instant messaging, emails and so on.
• Friends behavioral change: If your friends seem to feel uncomfortable around you, they may know something that you don't. A classic sign that your partner is cheating on you and you are the last to know.
• Accusing you: Another common sign you are being cheated on is accusing you of the very same thing they are so guilty of, cheating. They may drop hints that you are having an affair because their own guilt is starting to wear on them