The first sign that your boyfriend may be cheating, would be a sudden decrease in the time he spends with you .Also, if you notice that when you do spend time with him, he may seem to be distant, unhappy, bored etc... Also, if there is an increase in unexplained lost time. The second sign that your boyfriend may be cheating, would be an increase in arguments. If you and your boyfriend are suddenly arguing and fighting more often than usual. When the fights and arguments between the both of you are getting more heated, or severe, this is a good indicator of infidelity. The third sign that your boyfriend may be cheating on you, would be a noticeable lack of affection. If he holds you less, forgets to tell you he loves you, doesn't tell you that he thinks you're beautiful, doesn't call you by the cute pet names he has for you, etc...
The fourth sign your boyfriend may be cheating on you, would be a sudden lack of trust in you. If your boyfriend begins to question your behavior, and he starts hinting around at not having faith in you, there could be a problem. The trust issue actually originates from the guilt factor. Your boyfriend may accuse you of being unfaithful if he feels guilty about what he has done.
The fifth sign that your boyfriend may be cheating on you, would be the more obvious, suspicious behavior he may display as a cheating boyfriend. Suspicious behavior such as leaving the room for certain phone calls, ignoring certain phone calls while in your inescapable presence (riding in the car together), a constantly blank call history on his cell phone, a name of a person he never mentioned, and continues not to mention in his contact list on his cell phone (he could have her down as a he), he does not allow you to touch his cell phone for any reason, secretive text messaging etc...
The sixth sign that your boyfriend may be cheating on you, would be noticing his friends acting strange around you. Guys will lie for their friends when it comes to cheating, but that doesn't mean that they are comfortable lying for him, and it also does not mean that they are good at lying for him.
In a perfect world, boyfriends wouldn't cheat, but this is a far from perfect world. When it does happen, it hurts, but you do move on eventually. The best advice I can give to women who don't want their boyfriends to become unfaithful is, be the best you can be for him. Treat him with love and respect. Make sure he knows exactly how important he is to you. Be honest with him, be faithful to him, and let him know where you stand on what contstitutes cheating. Cheating can come in many forms. My idea of cheating is, doing anything you wouldn't do with your partner in the same room. I hope my advice can be most helpful.