<human>: I found out last night that my fiance of a year (In a relationship nearly 4) has cheated on me. He left his facebook open and there was a chat with suspicious content, which I then scrolled up on.
I texted the guy and he confirmed everything.

A bit of background: he is in the navy and I am not. He is regularly away for long periods of time. Currently he is back home with me every other weekend, which is nowhere near as bad as some separations we have gotten through.

When confronted, my fiance tried to lie his way out of it. I had to slowly add on to the question for him to realise he was rumbled.
I left for a drive that night, contemplated extremely stupid things, but basically just had some huge un-manly cries. 

Back in the flat today, I feel too numb to make a decision either way. He knows that I hold my morals so dear that he fully expects this to be the end of us, however I can't quite make that decision. I had been planning christmas at home with my family and him. All of our presents are joint-presents. I can't bring myself to ruin christmas.
Also an issue, all of the bills, the rent, everything is in his name. If I upped sticks, I would leave him in a lot of financial trouble. I can't do that to someone I love(d).

And finally, I just want to believe it was only the once, but he is far too convincing a liar (I now know) to ever be sure.
I want us to be as we were before.

What I would really appreciate advice on is whether it's possible, with someone you love, to ever get over something like this and have a functioning relationship again?
Do people ever stay with partners who hurt them this bad?
My mind speaks a lot clearer than my heart on the matter, but I find myself trusting each equally.

Summarize the given text in a few sentences.
<bot>: If a partner cheats one time, is that it for the relationship and everything you've built? Is there no way forward?