<human>: I'll try to keep it as short and simple as I can. I've debated posting this over and over.

My girlfriend and I have been together for a little over 6 years now and everything is pretty much all around fantastic. However about 1 year into our relationship I was offered a temporary position out of the country and not being particularly keen on a long distance relationship I broke things off. While I was away I hooked up once or twice with a woman I met at a bar. The sex was pretty underwhelming and it didn't go beyond the one or two times.

Flash forward to a few weeks later and my girlfriend and I have begun skyping. Maybe distance made the heart grow fonder, but we ultimately reconciled and picked things back up when I returned a couple of months later... Here is where I fucked up.

I am not remotely the jealous type but I must have been projecting because I began questioning and accusing her of sleeping with other people while we had been broken up. She earnestly insisted she had not and then volleyed the question back my way. I knew if I answered honestly it would be over. So i lied. It was too easy.

"We were broken up, I technically didn't do anything wrong! Hell I even got tested for STDs just to be sure there was nothing I could pass onto her. Besides the sex was bad and it meant nothing. Its almost like it never happened!" 

This is what I told myself, trying to convince my brain my lie was justifiable. I've told myself this for 5 years now and it's finally happened. I'm starting to crack under the guilt. I know nothing good will come of telling her, but in a relationship with otherwise 100% honesty this singular lie hangs over my head every single day.

I know if I tell her now she will leave me or all the trust she has in me will be irreparably shattered. But how else am I supposed to get rid of this burden?

Can you condense the text into a few key points?
<bot>: I slept with someone else while my GF and I were on a break. I lied about it and years later the guilt stills eats at me.