All I can think of is either:

1) He's grossly misunderstood the kink and thinks he's meant to be "playing the cheat" rather than actively involve you. In which case, another frank conversation is required.

2) He's embarrassed, shy or self-conscious about it and is uncomfortable with letting his Read more… partner read flirty messages with other women because he still thinks you may get upset

3) He's actually just cheating. But idk why he needs to if his partner literally finds it hot to see him with another woman. I can't get my head around that.

Rule #1: Never ever send anybody *** you've never met. Ever. Romance scams are absolutely rife in the BDSM community. From the male perspective, you're almost more likely to be speaking with a scammer than someone legit atp. If they ask for ***, you block and move on. If they ask you to book a Read more… dungeon that they give you the van details for, block and move on. Etc etc. Any variation of you parting with your ***, don't.

I think what a lot of people don't realise about sexuality is that fantasy doesn't always translate to reality; you may have obsessed about something for the longest time and then find you don't actually enjoy participating in it. But, you'll never know until you try. So, always approach with Read more… optimism but keep in mind that it's completely normal if it turns out to be underwhelming.

Relatively speaking, I think it's a very all-or-nothing thing, which means it's more likely than other niches to be a hard-limit for anyone who doesn't specifically hold it as a kink i.e. if you don't find it very arousing then you likely find it repulsive.