You know what, I bet more than half the guys on this website would not give 2 shits if the guy was in a committed relationship, as long as he was "willing" to fuck you anyway.
To be frank, the average gay guy nowadays live only for the sex so much so that even people in committed relationships are still considered fair "meat" for the taking.
The only reason open relationships work so well with gay men is so they can fuck around but nobody can "technically" be hurt because everybody involved knew what was going to happen.
Going from your post, even you writing "wrong" kind of insinuates that you say it's wrong because general society would say so but personally, and for most gay men, you might not feel it's that "wrong" as long as it's consented.
As I said though, just an insinuation from how you've put quotations around the word "wrong" so of course I could be wrong.
The unfortunate truth is that convenience and consent trump honour and loyalty.
Most of the guys on this website would probably encourage you to do, or say something like "do it, but you might regret it".
Bottom line is that most of them would tell you to do it.
Regardless of the encouragement to do so from other gay men, I suppose at the end of the day to each their own.
If you decide to completely stay away from the guy then kudos to you.
If not, well you're not going to be judged that much from the gay community since, as long as he's hot, they'd most likely have all done the same because at the end of the day, that's what really counts right?