Should I tell my friend about his girlfriend and my brother??

came home to see my brother (45mins ago) and seeing where he was at I went to his room to see if he was asleep and walked in on him and my best friend (been knowing since I was 2 years old) girl friend having sex. My mouth dropped now I am stuck in between a rock they begged me not to tell Franklin (my best friend) what was going on the past 8 months, 8 MONTHS this been going on, my brother also said if I was a real brother then I wouldn't tell Franklin and his girl friend begged me to the point where she had tears, telling me not to tell my best friend. Its just not right and I would feel wrong if I ratted on my brother cause we are real close brothers and I love him to death but I love Franklin just as much like a brother but I am caught in between a rock like I said and I need to know what to do. Should I tell my best friend or keep it from him and don't rat my brother and my best friends girlfriend out. Thank you guys

P.s My best friend and his girlfriend are getting married in 3 weeks this is crazy

Two options:

1) Give the girlfriend an ultimatum either to tell her fiancé about the cheating or you will tell him yourself.

2) You can keep quiet.

If you choose 2 then the affair will continue after the marriage, your friend (the husband) will find out eventually then the wife will tell your friend that you knew for x amount of time to try and deflect her guilt and then you will lose that friend for life.
If you choose 1) the friendship you have with your friend will be safe and will save your friend from MUCH more pain (imagine yourself in his future situation when he finds out that his girlfriend cheated on him and marrys him anyway and continues cheating during marriage). Therefore 1) is far more morally correct.

Now your conscience is thinking about your brother and the girlfriend however if they cared about you and the friend at all they would not have done this or have asked you to keep this a secret. They are trying to manipulate you (crying/using brother card) to get you to do what they want you to do. Sounds to me that I would value your friend far more than those two so the fact its your bro is irrelevant.

It will take courage to do 1) but in my opinion it is the right thing to do and remember the right thing is not always the easiest thing. Do not just tell the friend, give the girlfriend a chance to confess (it will give a greater chance to save their relationship).

I am only comming to these conclusions from the information you have given me. In the end it's your decision to make not mine.

You should tell your brother and your buddy's girlfriend to tell him, or you will. Give them a time limit and if they do not tell him, then you go ahead and do it. It will suck, and you should expect him to be upset. He may lash out on you if you end up being the one to tell him, but you have to do what you think is right. It's a sh.itty position for you to be in because you have your brother and your best friend to think about. However, think of what you would want if you were your best friend. Would you want to know about your girlfriend's affair before you married her?

Give them the ultimatum. Give them a strict timeline to do it. If they can't do it, then shoulder the responsibility of breaking your best friend's heart, but keeping his best interests at the forefront of your intentions.

so yeah my irst move here is to let them know that they are BEGGING you to LIE to your best friend.. do they realize that?
i would let them know. they are BOTH lying to FRANKLIN (and look right at the fiancée) - and you're marrying him in 3 weeks!

tell them that here are the conditions they must meet or you will tell Franklin. If they do not meet these conditions at any point - you go straight to Franklin.
1. they never see each other or sleep toegether ever again.
2. they never ever ask you to ever lie to your best friend ever again
3. one of them needs to tell franklin before the wedding.

any of those 3 things not abided to - you go straight to franklin.

sorry to hear about the situation.. this is not a fun place to be :(

I'm supposed to be hanging out with my friend tonite....might be a good time.

Seriously telling your friend the whole thing IS the right thing to do. This is in no doubt but I think Tobi is right as well. You should ask the girl to be honest with your best friend. I mean, imagine if you were Franklin, certainly you would wanna know the whole story, the truth!

UPDATE TIME FOLKS!....It went down ugly I ended up meeting up with my friend and got all of us together (my brother and the girlfriend). I simply turned to her and said "Ok this is your last chance tell him or I will" He didn't want to believe it at first. But when she admitted to it he took a while to respond. The girlfriend tried to say she was sorry and then my brother tried to say something to him but got beaten up..real bad I had to pull my friend off of him and almost got hit myself his girlfriend tried to blame me for everything and hates me now .... He is calling off the wedding and has informed his family about what has happened (this is gonna be an ugly month) it looks like my brother is going to need dental implants OUCH but oh well that's his problem, he and the girlfriend are not speaking to me either. The girlfriend called the police and my brother is going to charge him with assault and my friend got taken downtown SMH But my friend is sticking by me even closer than before:-) My parents and I don't think that my brother has any right to charge my friend with assault. Thank you everyone for the wonderful advice..I love this forum truly mature answers from everyone:-)

Depending on the laws in, where I assume is Mississippi, he could absolutely have grounds to charge your friend with assault. However, now that it's out in the open, the appropriate people know and are dealing with it. The girlfriend hates you because her façade is now ruined. So what? You did the right thing by telling your friend, you could have gone about it in a better way, but what's done is done and that's it. Hopefully you and your friend continue to stay friends and he stays away from the ex-fiancée. Your brother may have issues with your friendship, but that's also his problem and not yours.

ultimatum is the way i would go about it.
There is a reason why the girl cheats on your buddy
maybe he isnt good in bed or whatever
but he should know before the marriage
and 8 months is a really long time.

This will lead to drama. But in germany we have a saying that goes like this:
Better an ending in tears
than tears without an end.