How can I tell my boyfriend what I did with my ex?

They say that honesty is the best policy, but that ain't always the truth. Do you want to tell your boyfriend because he's inquiring or because you feel the need to unburden your conscience? Because if it's the latter, don't tell him. There's no good way to tell him, you'll only end up hurting him, and if this thing with your ex was a one-time-thing, then the discussion is over. You're not choosing between the two guys. But you need to sit with the guilt. I don't mean to be judgmental, but if you truly care for your boyfriend, you won't try to transfer this pain to him.

It may seem like I'm being cold, but look at it this way: Let's say you tell him. There are two options: he either dumps you or he decides to forgive you. If he forgives you, then you're more likely to cheat again. And then you'll be back to this point and faced with the same decision.

Hopefully you don't think I'm a jackhole for advising you this way.

Just tell him.... it may feel easier to do it over the phone but in person would be more respectful. let him know exactly what happend and how you felt and let him decide what he wants to do at that point. Be completely understanding for his feelings and know that he is hurting and you messed up if he wants to leave let him without question although you might be hurt you can not try to blame him for that so be open minded and be honest as soon as possible no one likes a dishonest person and without trust their is no relationship good luck girl!

I think you still have feelings for your ex or nothing would have happened. The thing is you gotta make a choice either your ex or boyfriend that you want to be with.