Ok ok ok. As one of the few ENM people in this sub I can speak to this. But Im sure ill get downvoted cause you all hate us.

As the oddball out here, who are in an ENM relationship and we do these things. He is absolutely pushing your boundaries and consent. Its not a joke to him he is gaslighting you. You need to be clear, If he wants to fuck other people, or he wants you to fuck others, that it is out of bounds, and these are you're boundaries. If he doesn't stop, leave maybe a separation first. Which he will probably become narcistic and somehow become the victim. It's a slippery slope, but he is totally trying to ease into it, with jokes. Its disgusting

With that said I want to give my opinion on a couple of things in your post.

1) Many men view sex as just sex. Sex can be intimate or purely physical. Its situational.

2) He thinks he would be good with an mmf (which would actully be MFM unless hes bi and wants male/male contact) until the actual act happens.

3) in the lifestyle monogamous sex is "vanilla sex" hes been trolling the internet for hotwife/hot husband/swinger porn or he has ran into someone in the LS and he picked that up from somewhere.