How can you tell if your girlfriend is cheating on ...

My friend is a real womanizer and he has no problem with women who use him to cheat on their boyfriend ( he won't do married woman though ! )any way he has five rules to know if a woman his cheating on some guy .

1- She's no longer as needy as she use to be.

2- She no longer gets angry at you.

3- She's being secretive about her whereabouts

4- She places the focus on your  part of the relationship.

5- She showers you with love though sex ain't getting better.

 What about just discussing your feelings regarding this, and rather than make an "accusation"...why not just discuss the issue and ask her?  Asking is different than an accusation. 

There's not a guaranteed way to "know" if your girlfriend is cheating, but I'd like to know what has changed that makes you suspicious? How are things different?

Are the two of you still close, in general? How much time do you spend together? How many interests do you share? Do you have mutual friends, as well as separate ones? 

Rather than accusing her of anything, have you considered trying to rekindle the flame between the two of you? Don't try to smother her, but be extra-attentive. Try to recreate the best part of your relationship, as you remember it, for both of you. It shouldn't be a chore, as I would expect that both of you would enjoy being together that way.

Do remember that emotional intimacy leads to physical intimacy. If you haven't been spending quality time together, really interacting rather than just being in the same place at the same time, I'd be surprised if your sex life hasn't suffered as a result.

If you feel a need to push for an answer, I'd suggest trying to set up a session with a therapist, and speaking with her about your concerns with the therapist as a facilitator. This is a really sticky topic, and a good therapist could help both of you avoid saying things you would regret for a long, long time.

Good luck!

If you are not a jealous or suspicious person by nature and you are having suspicions, you may be correct.  We all have what we call intuition and usually your gut feeling is right.  The only time it is not is when you are letting past experiences influence your thinking (such as being cheated on before).  Keep in mind that there are many levels of cheating with the first usually being an emotional affair, so if you are correct in your feelings, you may be able to catch it before it turns physical. 

There are a couple of clues you can look for that I have found to be good in determining whether something is going on.

Has she withdrawn?  Basically has her attitude changed to where she doesn't care about things you used to do together or calling you and checking in, if she used to do so. 

Has she all of a sudden changed her appearance, either dressing up, changing her makeup or clothing choices, exercising or losing weight.

Does she hide her cell phone/email/etc from you or keep her phone close to her at all times?

 Does she seem to make excuses for going to the store or running other errands (if so she may be using these to see him or to call him)?

If your girlfriend was cheating, believe me, you would know, when you have been with someone for so long, things change, maybe its you, try and spice things up, have some fun and if things dont feel happier, then its time to worry. Dont be so negative