Aware it's a zombie thread-
'Sex addict' is a fairly disputed concept and not all professionals believe in it, in particular probably not those with more formal and lengthy training, such as psychiatrists. It's not a physical addiction as such, like alcohol or heroin etc.
We've seen again and again on these boards how cheaters or porn lovers etc say 'I'm addicted' when discovered, in order to claim they can't help it, as a final excuse to be able to keep a cushy life,if they can't think of anything else.
Believe in sex addiction if you want, but also this is what sleazeballs say when they're discovered.
If you think about it, whether someone is a sex addict or not is irrelevant if the behaviour is the same as that of a cheating or sleazy wanker.
What mattered is if you are prepared to put up with what he's done/is doing.
If his behaviour (which you haven't gone into) upsets you, I would leave him if he does it again, not that you would necessarily know, so it's a matter of whether you can trust him and how much you minded whatever it is.
That you're seeking a group means you are finding it hard to come to terms with. That's not a failure in you- it's all on him. He should be doing all he can to help you feel it's put behind you- but a lot of women might not be able to put whatever-it-is behind you.
Maybe you could have individual therapy to help you think through how you feel about it all?