2nd reply. It's a hard thing to wrap my head around that a BF would actually enjoy that, especially if his GF is that beautiful. Apparently there are men that enjoy seeing their women get fucked by other guys, but I am not one of them. Nor would I want another guy to watch me fuck his SO (or any woman for that matter). It is not something I understand. And when I fundamentally don't understand something, it makes me very, very uneasy. I guess I'm just a prude, LOL.
In JAV, there are lots of "cuckold" movies where a guy get curious about what would happen if someone else fucks his wife. Those relationships never end well in those flicks. And I think it would end much worse in real life.