That sounds really scary just because you make a bad decision does NOT mean you are a bad person. In fact, because you felt so guilty about it just goes to prove that you are in fact a really nice person.

Sounds quite like a panic attack though. Have you talked to a counselor before? It might be more helpful for them to give you advice on how to better cope and find strategies to help it from escalating. What I find usually helps is just getting away from the issue (but that's not really feasible all of the time). Then again I usually have my panic attacks by myself so haha. I normally am fairly quick to recognize it and slow my thinking down and switch gears into something else. In any case, though it might be a difficult conversation I hope you'll reconcile with your bf. I would definitely tell him about what you were feeling early and maybe find a way to signal an anxiety attack, in the worst case scenario of it happening again so that way both of you can calm a little bit and stop the panic in it's tracks!