81% of women openly admit that they flirt with men they don't know on a regular basis, even if they're in a relationship or married. What this means is that although they may not go any further than flirting, the vast majority of women do find enjoyment in playing and leading on guys other than their boyfriends or husbands. It therefore goes without saying that some, unfortunately, will get a taste for that pleasure and actually choose to take it the one step further - which usually means going behind their partners' backs and sleeping with another guy.

So what can you do as a man who suspects their girlfriend is cheating on them?

If you ask her outright, she'll probably deny it, which is neither here nor there when it comes to uncovering the truth. The answer lies in finding hard, undeniable proof of her deception, so you don't need to directly ask her if she's being faithful to you. In this article, I'm going to tell you about a few of the different kinds of evidence you can look for.

1. She buys more new items of clothing than ever before.

Many women do this because they have a sudden new need to look and feel physically attractive (to the man they're seeing behind their boyfriend's back). You should keep an especially close eye on whether she buys new lingerie and underwear, particularly if she doesn't wear it around you.

2. Receipts.

These can provide you with a boatload of information if you can find them. When women cheat, their buying habits change. If it's not underwear (as just mentioned), it can be large amounts of credit for their cell phones or presents that could only be for a man (such as cologne, condoms, razor blades, etc.).

3. Unexplained extra mileage on the car.

If your girlfriend says she's coming straight home from work each day, or eating her lunch in the office instead of driving to a fast food place or some other eating establishment, don't question her outright. Instead, secretly take note of the mileage on her/your car at the start and end of each day. If she's using it to drive to illicit meetings with another guy, you'll see a stark difference between the distance she should have travelled if she were being honest, and what the counter on the car says in reality.

4. Strange numbers on the phone bill.

Unrecognizable numbers by themselves cannot be considered hard evidence that your girlfriend is cheating on you, but they can be possible indicators that something is going on. The best way to determine if a number belongs to a guy your girlfriend is secretly seeing is to check it against the numbers in your address book. If it's not in there, see if it's in your girlfriend's list of contacts in her cell phone. If it's not, try ringing it from a phone booth. You can either stay silent and listen to the voice that answers or pretend to be someone you're not and get a little extra info out of the person that picks up.

Lastly, always consider what your instinct is telling you. When a girlfriend cheats on her boyfriend, the first sign he notices usually isn't hard evidence such as the smell of men's cologne on her clothing or boxer shorts in her purse, it's a "feeling" in his gut. If you have this feeling, consider looking for hard proof like the examples I've told you about and others. And, importantly, don't confront her until you're sure of what is or isn't going on.