Well, the poster and his sister "woke up crying" and feel really guilty about this booty call. So now he poses the proverbial question: Should he tell his boyfriend or live with the guilt in secret?
1. You's a ho. Ho.
Okay, like, first off, sisters don't fool around, so ya'll are definitely not sisters. Me and my "sister" have made out a few times here and there, but that's about it. No big deal. One time we took a shower-bath together, but, nothing happened.
Basically, you's a ho, well, okay, I take that back. You're more or less a ho, than a man. Now I can see where you get love/sex turned around, but still, if you loved your boyfriend as much as you said you do, then you wouldn't have done the dirty, wrong, unforgivable thing that you did.
If you tell him, he'll dump you, maybe.
If you don't tell him, that guilt is stuck over top of your head. So, um, basically it's your decision. I would want my boyfriend to tell me if he did something like that. So that I could dump his ass.
2. You both woke up crying? I think that's a bit dramatic, but i guess that's what "girlfriends" do together.
Anyways....about the issue....
Keep your mouth fucking shut and get over your guilt. You yourself said it didn't mean anything so what the fuck are you so worried about? What he doesn't know won't hurt him. He'll most likely do the same thing to you at some point in your relationship so i wouldn't think much on it.
3. if i were your bf, i would not want to know.
telling him is basically making it his problem. instead of only you feeling shitty, you will make him feeling shitty too.
if you are sincere in your remorse, just do not do it again. remember how it made you feel, maybe this will help you stay out of trouble.
and no, complete honesty is not the best policy.
4. There's no such thing as complete honesty, just moralists with limited self-knowledge and a projectile masochistic streak. And jealous partners trying to control each other.
If you want to punish yourself, go for it. You don't get any points for it. But no need to hurt the b/f doing so, which would be cruel and self-centered. He's almost certainly not going to accept your indiscretion with magical forgiveness and saintly aplomb, so there's nearly zero chance of that sort of bad-story outcome, either.
You're stuck, but life goes on and your personal suffering will dissipate in short order. There's no redemption in feeling bad about it, but then, no forgiveness is needed. Just live with it; learn that restrictive sexual commitments are never as solid as anyone pretends (gay or straight); go on and try again.
5. Having a healthy relationship with someone means being completely honest. Whether that be good or bad, there is no exception. If you don't tell him and it comes out later down the road then he will wonder what else you might have been hiding from him.
Be honest and upfront now, if you really do care about him it is the right thing to do.
I'm sure my advice won't be the popular choice but if you're an open book to him now he'll know what to expect down the road. He'll know when you tell him things it is the truth and he won't have to second guess you. Whereas if you opt not to mention it, him finding out later would definitely deliver a severe blow to the trust category that both of you might never recover from.