Yeah he was monumentally stupid. Everyone knows if you’re going to role play you keep it safe, by not making it too close to home!
Rationally I know that my DH will find other people attractive from time to time, and in amongst them will be some of my friends or people in our social circle - and I’m actually perfectly okay with that, but I’d definitely be very upset at actually being told about it, so I understand how you’re feeling.
Similarly, there has been a man or two that I have found very attractive/been drawn to/had a slight crush on for a time, in the time I’ve been with DH. I see that as perfectly fine, perfectly normal, and really not a problem. It doesn’t in any way diminish or take away from the fact that it’s DH that I love, am madly in love with and still very much fancy. So I would afford him the same right to an inner world as I allow myself. But I wouldn’t want to know about it, and I’d certainly never hurt my DH’s feelings by telling him about men who I find interesting/attractive!
This is the difficulty with any kind of ‘fun’ sex/fantasy/play. It can very quickly become not so fun.
Hope you manage to get past it (if you decide that’s what you want to do). If he’s a good, decent man and has always treated you well then I think it’d be a shame to let this ruin it, and you can probably come back from it. Maybe just don’t play any more of this type of role play game as I don’t think it’s right for you!