Hi there. I hope I can help.
Firstly, please allow me to say that I am sorry he has put you through this...this is something no one deserves out of a partner, and I am sickened and appalled by his behavior. The line about him going because you "don't fulfill his needs" is a load of (your word here). By putting it back on you, he makes himself feel better. Understand that this is NOTHING you have done or caused. This is entirely his failing.
He MUST stop seeing this women immediately if there is hope of saving this relationship. If you decide you want to work through this, you have to understand that it is going to take time...forgiving him does not mean that the emotions vanish. You need to be patient with him and yourself as you try to work through things, and he must be patient with you. Additionally, he would need to prove, without question, that he knows he was wrong and that he is committed to this working. That takes a lot of time and effort out of the two of you. If one of you doesn't fully give in trying to work past this, it will fail. I have to confess here that I am not entirely confident that your husband will put forth what is needed...him "not believing in therapy" is, to me, both ignorant and a cop out.

He has to be willing to do what it takes to save his marriage.
That is, of course, if you wish to work through things...I do not like advising married couples in what they should/shouldn't do in regards to staying together or divorcing, but your husband's callous behavior is grossly disrespectful to you.

If you chose to leave, Lee gave fantastic advice that I hope you can follow.
Please know that you have my support in whatever you decide. Know that I am praying for you, and that I wish you my best.
Hugs,
Harley