Personally I don't mind porn in moderation and watch it myself.
Adult work is something entirely different.
It would be important to know if the history is really due to pop ups on porn sites or whether he went on adultwork either directly or purposefully clicked on a link from eg a porn site.
If either of the latter .... He purposely went on adultwork and that means he's purposefully browsing (at the very least).a sex work/prostitution site.
The "caught chatting & flirting (and sexting?) online with other women" is disturbing.
You say you sorted it out but to be blunt, you don't "sort out" someone flirting (and sexting?) with other women ..... It's a type of infidelity and the partner who accepts it is a victim of infidelity. The partner who did it doesn't really suffer any consequences. Nothing"s "sorted" in my book. They just got away with it and are probably inclined to behaviour like that.
It reminds of lots of women on here who say "we got through it" about their partner cheating on them. How did "we" get through it, it wasn't something that somehow happened to you both; it was something immoral and disloyal that one of you did to the other.
These men often repeat similar behaviour. When there's an unhappy woman on here, talking about unacceptable behaviour, there's almost always a background to that behaviour.
For me, it would be instrumental to find out if those hits in adult work were truly pop ups or if he's browsing a sex work site.
(Having cheated before - let's call a spade a spade).
I wonder if you, not him, had been caught doing all that "silly" flirting etc. with other men, if you'd still even be in a relationship.