I think his willingness to change is admirable, and as far as you know he hasn't had any slip ups since?

I think its pretty gross what was going on, especially the group sharing stuff. Its probably hurting you that its 'real-people'. Would you have the same reaction/hurting if he was just watching porn?

I think you should keep giving it a go, but be on high alert. You also *need* to try let go from the hurt, else that'll drive more issues between you two. Right now its been found out, you've made your feelings clear and actions have been taken. Until he breaks your trust again, I think you should give it a chance. 

Will all that being said, if you can't move past it, which is fair. Then maybe in a month or three, re-evaluate and make a decision. There's no point dragging on a relationship where you feel disrespected and seen other woman disrespected and you don't believe he can change. He probably doesn't how the actions made you feel, because with a lot of guys it takes an event to make them realise how discussions of that nature really do disrespect and affect woman. He's had his lesson, lets see if he learns. 

Best of luck OP