This is all written with "normal" relationships in mind, where it is assuemd, that both parts would very much not like the other to fuck around. If people have an open relationship, and have agreed that it's fine to fuck other people, no harm is done, and it's not really cheating.
It's a very disrespectfull act towards your partner, you're betraying their trust, and without a good reason. Lots of other things can have a good reason but "i felt like getting my dick wet" is not one of them.
It's not much different from having sex with your best friends girlfriend/boyfriend. you're betraying their trust, quite possibly ruining your relationship with them for good, and over what? an hour of enjoyment?
If you think about it, any instance of cheating on your partner mentioned forther down in this post, can be swapped with fucking your best friends partner.
You may think, but hey, it's not such a big dea
l, it's not like shit has changed just cause i fucked someone else, but it matters to your partner, most likely it matters a whole fucking lot, and if you're willing to do that to them, just for a quick bang then you should really consider whether or not you actually give a shit about them.
I'm willing to say that most likely, you don't if you cheat. Eitehr that or you're a) too stupid/egocentric to realize that just cause you think it's not a big deal they might not think so. or b) too god damn retarded to think about it, and controll your lust at all.
"It was an accident, and it didn't mean anything" are probably amongst the lamest excuses ever, how did it happen, was you lying peacefully on your back, naked, with a hard on when she just passed by accidently, naked, and she fell and landed on your dick, and then an earthquake came and started rumbling things up, and you accidently came?.
If you're unable to controll something that simple, you're nothing but a slave to your instinct, like animals, and i wouldn't treat you with more respect than i do animals.
If you honestly doesn't care about your partner, maybe you're just with her/him to have someone to bang or something, and don't really see them as a friend outside of teh bed, at least have enough fucking honor to break it up with them before sleeping around.
Don't keep someone around just for comfortable security, without really giving a shiot about them, thats really weak, and only shows that you're a pittyful person, without independence.
Relationships are hard to be in without somehow hruting your partners feelings, eitehr when you break up, or because you're not what/how he/she wants you to be in one way or the other, or in other ways, and you can't totally avoid that. When you break up with soemone, they most liely get hurt, it sucks but you can't really just stay with someone you don't wanna be with just to spare their feelings, that would be stupid. But you can keep your pants on, it's not liek you're beeing asked to give away your freedom or the rest of your life (as in stayign with them forever, from the break up example) You're just beeing asked to say to to a mere moment of pleassure, because it would hurt someone who you're supposed to care a lot about a lot. If you can't even do that, you're only proven that you really don't give a shit about anyone but your own sorry ass.
If you want to be with many different partners and not be bound to one, no problem, just be honest about it, and don't engage in a romantic relationship with any of them, while keeping them in the dark about how you're with others as well. Sure a lot of potential bed-partners might pass on you, if you're not gonan be exclusive with them, but if you see this as an excuse to get involved with them while cheating on them behind your back, it proves that you're nothing but an untrustworthy coward, who lacks too much compassion to give a fuck about anyone but yourself.
Bottom line, be honest and good to the people who are supposed to be importnat to you (your partner, your friends etc.) and if they'r enot important to you, don't pretend they are just to get your own way.
TL

R: cheating is wrong, and like fucking your best friends wife. don't comment if you can't be bothered to read.