What do you do if your girlfriend dated your cousin's younger brother and hid it from you but you found out and dealt with it and remained together but after you broke up you found out they had sex?

to begin with 'your cousin's younger brother' would be your cousin as well,so I'm thinking this is just a BS question,but ennyhow..............

Cousin,the key here is found in your question!

read the words...."after you broke up"....so,what do you DO?

N O T H I N G !!!!

you two are no longer a couple,you're broke up,two separate people!

It would be like finding out your neighbor had sex with her dentist>>> it ain't yo' problem!

it wouldn't matter if your ex OR your neighbor had sex with the entire Seventh Fleet!

not your current mate,Not Your Business,period.