So my cam using ex said the free bit was like a strip bar. The guys hang out and text chat in the room, the "hostess" hangs around flirting.
The sites run on using tokens to pay for stuff, on the "free" rooms the guys can donate tokens to pay the hostess to do something for the group. Or they can pay for a private session which will basically by cyber sex. I think it used to cost my ex £40 a session.
The site he was on, I got into his phone while he was logged in and via the account page was able to see all the dms he was sending women and also the financial history of where he'd spent tokens. It was very very obvious he was doing a lot of private sessions.
I expect your ex will have locked that down now. The other thing you can do is do a Google search for his username on the sites. Search site:webcamsexample.com usernamedickhead
The camgirls leave reviews, basically I think saying who will pony up tokens so they can block freeloaders from their rooms. So if he has a bunch of high reviews he'll be paying.
I tried to forgive my ex as he did the whole "it's just porn and you are fine with that, I'm an addict I can't help it blah". But I'd lost all trust and felt like I didn't know him any more. 5 years later I found out he was still doing it so I left.
My advice would be get out now. The fact he's on those sites in the first place tells you a lot about his attitudes to women and sex, none of it good. I wish I'd left the first time though so I'm probably biased.
Good luck op and DM me if you want to xx