Yeah, would be a deal breaker for me.
Firstly the exploitation - they're all exploited in one way or another, not as in the girls are all trafficked, but financially, when you are on those webcams, the owner of the site takes so much of a cut from what you earn. When you do well, you end up getting forfeited for the most stupid reasons, such as they'd do a random view of your camera and notice the sound quality or picture quality didn't match their expectations or the lighting wasn't adequate or you said something they didn't like... so they'd make deductions from your earnings.
Also, to be a webcam model/entertainer or whatever, they request a copy of your ID. Fair enough to prove age, but I know for a fact they sold images of mine...
I did it about six years ago as I was a bit of an exhibitionist and got a thrill from it until I understood how degrading it was. The men who watched were ALL trash, no exceptions. They believe they pay and therefore own you for a specific time. The girls have to be nice otherwise....financial penalties and deductions from previous earnings (they don't pay out until you get to certain amounts so they always have your money to hold you to ransom). It's just disgusting, I'm glad I grew up.
I don't know your position with your partner, but paying to view a person does reflect on him and shows how he views women as sex objects. I hope it's not family money he is paying. He could be spending that on you....the real thing!
I wouldn't say it's cheating, though we all have different boundaries of what we would accept in a relationship (I wouldn't accept my husband doing this), but if he paid a random woman at work or in a club to undress for him and speak to him sexually, would you consider that cheating?
Also, sorry you've caught him doing this. It's no reflection on you, I'm sure you're stunning and you're right there in front of him and he's been a dick thinking with his dick. Do you really want to be with someone who views women like this? Either way, I wish you well. X