If i was personally in this situation, I would want to own up to it because think if he hears it from someone else because that will cause more trouble than it will already. Being in a relationship is about being honest with your boyfriend because otherwise he might think you are lying about other things. I know it won't be easy to admit that you slept with his best mate however he has a right to know, even if you were drunk it's not an excuse really because to some extent you should be able to control yourself. Also you got yourself into the situation by drinking around him.
You're likely to feel guilty because you love your boyfriend however if you love him enough you won't want to keep this from him as honesty is sometimes the best policy and in this case it is.
When you see him just talk to him, and tell him you made a mistake and that it's really difficult to tell him however it needs to be said otherwise you will be lying to him.
DON'T EVEN THINK ABOUT KILLING YOURSELF! Just because you made a mistake its no reason at all to even think about killing yourself so get the thought out of your mind, it gets you nowhere in life (literally) you have more to live for that killing yourself over the guilt of cheating. You need to seriously think about the fact you even said that because it's no wise. It's something serious and you seem to say it over something so little. (sorry this might seem like a rant but it needs to be said)
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