This is a toughie. Some hard hitting advice that perhaps all men approaching 30 will need.
You'll hear it in bar rooms sometimes. "Monogamy is outdated." Whether that's true or not, time will tell. However, if you are in a monogamous relationship, I think it is better to uphold it than become disloyal.
The main reason, of course, is because of morality. If you don't want to be cheated on, don't cheat. It is simple. But the other reason, perhaps a better, more important reason in my opinion, is that you don't want to lie to yourself.
Monogamy is a structure. And it is your choice to follow it. If you stray from the structure, you'll have to find a different structure. I'm not here to tell you what is right or wrong. But what generally tends to happen when you stray from a structure is that you lose faith in it. And when you lose faith in one structure, your entire foundation becomes shaky. You begin to do things that are neither here or there, you question your morality.
The "crime", so to speak, isn't about questioning morality. That is a process that needs to happen, in some level, in some shape or form.
The "crime" is not being able to follow through on what you believe in. The only time a person is really capital W wrong is when they are not following their own values. If you are in a monogamous relationship, you are basically considering yourself to be part of that value.
Here are a couple of things to consider.
The number one thing I notice about people who cheat all the time is that they aren't attracted to their partner. This is a huge mistake. No matter how kind, rich, funny, etc. your partner is, if you are not attracted to them, remain their friend, not their lover. You are depriving yourself and the person you are dating.
Secondly, try to make sure you are with someone who has roughly the same sex drive as you. If you are not, not only will you not want to remain faithful, but you will also feel like the relationship is a trap.
An ideal relationship, from my perspective anyways, is when both your needs are being met. Making sure that your sexual needs are met is a very necessary component to ensure your monogamous relationship is a success.
The worst thing you can do to someone you love is to hurt them. I always think of that whenever I get any sort of temptation. I also have martial arts, running, gymming, tennis and swimming to fall back on. And poetry. Any excess sexual energy can be used to work out or aid in the process of creating something that needs it. This kind of sublimation is a cool part of growing up, and I urge you to experiment with redirecting your moods and using them on activities that are different.
With all this comes knowledge of self, which is a big boon, and knowledge of your body, which in turn helps with the knowledge of your soul. For 95% of the cases, I would say what I have mentioned above is good advice.
However, for 5% of these cases, see a doctor. Maybe you are a sex addict, and truly need to deal with it. If that is the case, therapy is a great and useful option. Either way, communicating with your partner helps ease the stress and may even bring you closer together.
I know these things are tough, which is why I wanted to write about it.
Of course, if you're polygamous, do whatever the hell you want. But remember, there are pros and cons to everything.
Don't be so quick to disregard a structure that you don't fully understand.