Should I tell my boyfriend that I cheated on him?

There's not anything you can do to justify what you did. You have to tell him and then let him decide what he wants to do. If you really want him, you have to stop the bullshit and let him go. Like that proverb thing goes - if he comes back to you he's yours. But seriously cheating and lying is completely anti-cool. I'd probably kick your dog.

I can tell you right off the bat that whether or not you decide to leave this guy, the cheating needs to end.

As for telling him or not telling him, I'd say tell him sooner rather than later. We all learned as kids that continually lying to our parents only led to worse trouble than it would have if we simply just came clean in the beginning. The principle is the same here.

As you pretty much said in your question, being cheated on inadvertently led to you cheating on your current boyfriend. This is a behavior I've heard referred to as 'sabotaging' a relationship. You've had chaotic relationships in the past and for some reason or another there's a part of your mind that clicks in that chaos is what's supposed to be present in a relationship so you end up inviting chaos in if it doesn't happen on its own.

And with all this talk of pregnancy flying around I'm going to go ahead and say that you need to be responsible about this and tell him and/or settle this chaos creating habit before you even think about bringing a kid into the world.

Wow, the tables have turned! I don't understand how someone who could be so hurt by something, and then turn around and do it 4 times. That's just nuts. You need to tell him, and you need to break up with him, because honestly you don't deserve him, and he doesn't deserve to be cheated on.

I think that you should definitely come clean to your boyfriend about the cheating and as far as the Update: Once you tell your guy that you have cheated you may not need to make the decision. If you love him then explain yourself (whatever that may be) but I definitely don't think you should just break up with him to avoid an awkward situation,besides once you tell breaking up with HIM might not be an option.