"It just fell in I swear!"

Is your sister your twin and did she play a switcheroo? Cause than it's entirely plausible it's an accident. And I guess accident means that neither of them planned on it happening, but then it just happened. Either way it still sucks to be you. FYL OP.

be glad you've seen his (and your sister's) true colours before you gave him anymore of your love and commitment. get over it asap and start looking for the One who deserves you. good luck OP :)

Don't you just hate it when you trip and fall into a ******!

You could "accidentally" crash his car

sweet accidents ;) sorry for u baby

how do you "accidentally" sleep with someone?

I hate sisters who would do that. -.-

I really hate reading FMLs like this. That's really ****** up that your sister did that. Same goes for your boyfriend. Hopefully ex-boyfriend now, if I might add. If one of my older sisters ever slept with a boyfriend of mine, I would flip shit on them. That's not only disgusting but it's extremely ****** up. I think she deserves to get slapped in my opinion, maybe something a little more severe to get it through her head that she's a nasty ***** that shouldn't take what's not hers. But that's what I think, do whatever you want, she's your sister. Good luck with the both of them, OP. And trust me, you don't deserve nasty ass people like that. Find someone better.

Then "accidentally" burn his stuff and accidentally" knee him in the balls