I had sex with my boyfriend's brother.

Tell him. If he leaves you he leaves you. You just have to hope that things will work out. If you don't tell him and he finds out down the road the hard way...then it won't end for you as well by any means. Bite the bullet now.

the one real thing to do is to communicate with him and if you thinks he's the 'one' then I don't think he'll want to break up with you but def be mad at you

Just say because you were drunk you got confused and thought it was him

I wouldn't bring it up. He is not going to be understanding.

Oh, btw, are they identical? Were you confused about which one you were with?

I wouldn't tell him if it was a one time stupid thing. but you have to make sure it never ever happens again. I think it would hurt your relationship and the brothers relationship. both you and his brother have to live with what you done. sometimes people wanna tell so they can feel better about things...about being honest. but I don't know if it like is really good or not. cheating is wrong. always. however it something stupid happens. I dunno. maybe its not best to tell. if it is going to come out, then I would guess it would be better to tell him right away. but if you and his bro are not going to ever tell. then I wouldn't say anything.

You have to tell him, you did wrong and you have to fess up to it. Trying to cover it will only make things worse. His brother will probably end up telling him at some point and then he will definitely want nothing to do with you.

I personally think honesty is the best policy, I know that I couldn't live with myself if I did something like that so will you actually be able to lie to him everyday.

Its gonna be an awful feeling but you should treat others how you want to be treated, wouldn't you want the same respect from a guy you're dating to at least be honest with you?

I know this may sound wrong, but I seriously just wouldn't bring it up. It's not like intentionally did it. Yes it was wrong, but I think you should just put it behind you.