I'm so sorry, honey. It's a terrible thing when you're cheated on, and it doesn't matter whether it was a BDSM relationship. Do you have any friends or family you can talk to? They don't have to know about the nature of the relationship you had; you can just tell them that your boyfriend cheated on you, so they can offer some emotional support.

Just hang in there and keep on going. It'll hurt less as time goes on. As my mother always says to me when something awful happens, "this misery too shall pass."