So, you're in a relationship that is not 100% satisfying you.. but you're too scared to actually talk to your girlfriend about it and maybe try and liven things up.
You decide you want to cheat instead.. because as you put it monogamy is a 'concept' and does not over rule 'instinct'... yet you're too scared to just do it and get caught.
You make a thread looking for help on how to not get caught.. yet you're too scared to not go anonymous.
tbh, you won't need to pay, you must be fighting them off.
Monogamy might just be a 'concept' but if you don't agree with it don't be in a monogamous relationship. And don't say you 'agree with it, but man has needs'. You either do, or you don't.
If you wanna sleep with other people, at least break up with her, or give her a chance to level the playing field by finding other guys too. Tbh, I can't imagine you're that good in bed anyway, what with the lack of spine and all...
Get advice and answers to your Qs here