You are amazing. Wish i had your strength
I'm not "stronger" then anyone else.
To not sleep around with someone is just as easy as not stealing a motorcycle that just stands somewhere with the keys on the ignition.
There's no such thing as "we accidentally had sex".
There's no such thing as "we had sex because we couldn't control our bodies".
Personally, I don't mind off course. Sleep with whomever you wish for all I care (although sleeping with someone who's already in a relationship, married or otherwise, is seriously unethical). But be honest about it. Don't come crying that it was "an accident" or "uncontrollable" or that "it couldn't be avoided".
That's utter nonsense. You knew very well what you were about to do. You were very aware of the decision you made to go through with it. It was a conscious choice, a decision, to engage in a specific act. A decision that you could have
easily walked away from, if you wanted to.
But you didn't.
I'm not saying your should apologize for it. I'm not even saying you should regret it. That's all upto you. I'm just saying: be honest about it. Don't come with lame excuses that make no sense.
You did what you did and you were fully aware of what you were doing while you were doing it. You could have decided against it, but you choose to go through with it anyway.
That is fully your responsability. You didn't slip and fall on her.