Despite what I said in my previous post, I wouldn't advocate cheating for the following reasons:
(1) There is a very high probability it will change your behaviour, so high that it's practically guaranteed you will become more secretive. You will act differently around your girlfriend. She may or may not pick up on it -- doesn't matter. The point being is that if you cheat, you now have something to hide. In order to hide it, you have to act with deceit. You will have to create and maintain the illusion that she is in a relationship with a loyal man -- this is deceit, because you are NOT a loyal man. Deception is the opposite of the integrity. If you cheat, you are sacrificing integrity & loyalty for a few moments of pleasure due in large part to your lack of self-restraint regarding lust.
(2) There is also a chance she finds out that you've cheated and confronts you. Do you then lie to her face, or do you tell her the truth? Do you go all-in on the deception at this point, or do you come clean? Do you expect her to dump you, or do you expect her to stay with you? If she dumps you, are you okay with that? If she stays, are you okay with being with a doormat who has low self-esteem and can you look her in the eye knowing what you are putting her through? If you cheat, are you prepared at any given point to have the relationship with your girlfriend end permanently? Are you prepared to deal with the life changes that will occur and the social backlash you will receive? The implications of these questions can be completely avoided if you choose not act on your lust.
(3) STDs & pregnancy. Having sex with someone ALWAYS includes the risk of pregnancy or getting an STD from that person. You may be okay with cheating, but would you be okay with giving your girlfriend a permanent STD? Are you okay with knocking up a chick outside of your relationship and attempting to navigate through that in secret behind your girlfriend's back? How would you feel or react if you were loyal to your girlfriend and suddenly you contracted herpes, chlamydia, warts, or HIV seemingly out of the blue?
(4) Hypocrisy. Self-explanatory. You wouldn't be okay with your girlfriend cheating on you, or if you found out she's been cheating on you the entire relationship. Yes, there's a double-standard in the manosphere that suggests men and women cheat for different reasons, but if you "don't care" about moral things, then you logically also wouldn't care about the moral implications of this double-standard.
(5) Conscience. Can your conscience carry the burden of the act? Morals play a role in this, as does identity. This involves the reputation you have with yourself. By cheating, you are changing the reputation you have with yourself. How will you reconcile the fact that by cheating behind your girlfriend's back, you are explicitly demonstrating that you are a disloyal man who lacks integrity? Maybe you will be able to self-rationalize yourself out of feeling guilt, just the way you are self-rationalizing yourself into cheating. Perhaps you're on the spectrum of sociopathy (such as myself) or psychopathy, and are incapable of feeling such guilt, or at least do not feel it as strongly as most people. You may think you know how you will feel after cheating before you cheat, but you will ultimately find out for certain once the deed is done and irreversible.
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TL;DR
When you cheat, whether you are discovered or not, you violate your partner's trust. You needlessly expose yourself, your girlfriend, and the relationship to unnecessary risks. You sacrifice your loyalty and integrity for a fleeting desire of lust. Cheating also demonstrates a lack of restraint, questionable priorities, poor judgement, and it reveals countless other negative qualities about yourself.
Moral arguments aside, cheating is just not a sensible act. It's not a wise decision from a rational point of view.
I recommend not cheating.