[rob]

I don't mean to go on, but you aren't keeping the pain away from her. As you said, you prayed to God that to say you wouldn't make that mistake again. It's affecting your behaviour. She'll notice.
Also, if you aren't telling her about this time, then what's to stop you cheating again and not saying. You'll be amazed how easy it is to break a promise that you promised to yourself.

And her friends and family don't need to know; you weren't cheating on them. You won't lose their respect if they don't know.
And what better way to improve courage than to tell her?
In your first post you said you hoped it wasn't cheating, but you seem to be doing everything you can to avoid stopping it being cheating. Beagle and Scarbowl said to tell her, Dan and Jennifer say communication is the key to a healthy relationship. Their definition of cheating, a breaking of trust, applies here too. If you really don't want it to be cheating then swallow your pride and tell her. If you really are scared that she'll break up with you/tell her parents and that they'll lose respect for you etc then how has your relationship lasted this long; if you don't trust her enough to keep a secret which you are genuinely sorry about?

However, it is down to you in the end. Just think about what we've said.