The very same thing happened to our family just over a year ago.
(We've been married for 6 years).
My husband got involved in pornography when I was pregnant with our first child (7 months into our marriage) - I don't know if he ever stopped after that as I never 'caught' him in the act but I think he must have as he slept with a prostitute 2 months after our second child was born.
It's been about 18 months since that aweful day.
The interesting thing is that I don't dwell on what he did (yes, it does cross my mind) but I don't feel hatred, anger, resentment etc. I don't speak to him about it (we did that the first month and then I let it go - I want him to have the chance to put this behind him and be free of sin. I want to give him the opportunity to forgive himself) - he's in a lot of pain as a result of this and my heart aches because he is still a Son of The Father with potential to be an heir in the kingdom...
The problem is not so much what happened that night ... but rather, what happened after that night.
At first he felt remorse, fear of losing us, losing his membership etc.etc. all good things for someone on the repenance path but then he started longing and intiating sex in our marriage ... every time I pulled away ... he felt rejected and got angry (which resulted in temper, outbursts, insults, threats to get divorced - he does so on a daily basis (the threatening to leave part)
My heart longs for that person he use to be: the gentle, caring, sensitive, sweet and kind man.
I have lost every desire to be intimate, we have no relationship, no friendship, our only link is to our children.
Why am I still married to him?
Because of counsel from our leaders - bishop in particular, my belief that the Atonement can mend ALL things and wanting to be obedient to the covenants and promises we've made when we got sealed for time and all eternity.
It's an incredibly hard road to travel but, a part of me just can't give up on a sealed family.
I love my children - and if it wasn't for them ... I probably would have left already.
I wish there was any advice I could give you (and myself for that matter), I wish I could show you what to do ... how to make it work.
All I know is that living a gospel centered and righteous life ... remaining steadfast and immovable so that YOU can have the comfort of the Holy Ghost is what gets me through this...I am still a happy, peaceful person and believing person despite what the future holds.
Good luck katiekins ... my heart aches for you, I feel your pain and pray that you and I both (along with our families) can get through this.
*hug*