Wow I really like your explanation. I sort of what to explain what this was regarding further now and see if you have any other advice -

I am uncomfortable with his relationship with his female best friend. They've sent each other nudes, she calls him baby, and they've always had an incredibly flirty dynamic. I finally confronted him about it and he said he does like her and he believes she likes him too, but they determined they would not date because of distance and a few other reasons. He also said he would cool it with her.

I've already discussed with him how I would never want him to end a female friendship and I will stay mindful of any emotions of jealousy so I'm not ever emotionally manipulative and I will be honest and straightforward about what I feel so there's never misunderstandings.

When he told me this, I said I was shocked he would want to maintain such a close friendship with someone he liked this way, and I asked him how he would feel if I had this context with a guy and that was when he was like basically, I'm emotionless and I know I don't have anyone to feel jealous over. (I just moved so I don't know a lot of people where we live and he's aware of that i guess)

He also confessed that he had two ex girlfriends cheat on him with THEIR male best friends, and one of them had made him cut off his female best friend because of jealousy and he said he would never let this happen again and he wasn't going to ignore or stop talking to this girl. He also confessed to having felt jealous of these guys before they cheated.

I won't go into full detail of what happened with his exes, but them cheating on him with their male best friends sounded traumatic and it's almost as if he's made himself emotionless about this as a defense mechanism.

I don't know how anyone could not fear cheating or have bouts of jealousy when ones partners friendships of the opposite sex are a certain context?