Fiance keeps watching porn

Asking for a friend...

After agreeing on having him not watch porn anymore because honestly it's quite disrespectful towards us ladies (except if both watch it together, but that's not the case here), this guy kept on watching porn and worst, lied about it. Pretty big trust issue here. Fiancée found out by chance which let to some more investigating which shows a lack of trust. (Understandable after all he lied). How to approach this conversation? It's not enough for a break-up but it's still pretty messed up.