Some advice would be lovely?

So my girl and I have been together for 6 years. About 1 years ago we had to do long distance for a while (I was finishing up school and then). So while I was at school she started hanging out with this guy from work he was her best friend or whatever which naturally concerned the hell out of me. We had several fights about it but she managed to convince me that everything was ok.

Come to find out (after I'd graduated and we moved in together) that they had become romantically involved. She was out of town for a while longer for a job and was apparently sending him dirty pics and ended up blowing him once.

She did come clean about it within the hour she says she feels like the biggest piece of shit for it and seems genuinely sorry. And we have decided to try to work it out. But it's so freaking hard..
. any advice would be appreciated.
Some advice would be lovely?
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