This whole thing is beyond complicated ladies, she is in a tough position here, so whatever you do, please be nice to her. But absolutely do please keep telling her this is not her fault. And SDarvasi, if you can't be nice, go be mean somewhere else, she doesn't need your mockery.
There is no excuse for cheating. He will want you to take the blame so he doesn't have to even though he is the one who cheated. There were other things he could have done... he could have told you it was a problem so you could either have sex with him more often for his sake even if it was beyond your own sex drive out of love for him, or you could talk to your dr about your sex drive to make sure everything is ok, or you two could have gotten therapy AND at any point he could just jack off without any cheating at all.
If he doesn't want to be with you, it would have been more respectful and kinder to just tell you so to set you free to be with someone else who WILL cherish you and make you a priority.
I would NEVER forgive him, cheating is a lot worse than him having sex with someone else, it's basically proving that you are such a low priority to him, that his Temporary instant gratification is more important to him than your long term suffering and feelings and trust and the health and security of your relationship with him.
I am a strong believer in that you are settling for less than your own personal best of what you deserve if you allow your s/o to be less than what you give to him or her. For example if you are 100% faithful and loyal then you deserve that in return!
I am so sorry for the pain and suffering you must be going thru. I would take this as an eye opening opportunity now that he's proven with his actions how he doesnt cherish you or value you the way you deserve, to leave his sorry ass and when you do start dating again and looking for a s/o try to find one who has a sex drive more like yours (they are out there I promise.)