Do my feelings even matter?

So I have been with my bf for 6 years now. I like pretty much everything about our relationship, but there is one thing that I hate and can't shake. He has this one thing that turns him on or whatever. I feel stupid even saying it. He likes to think about me with someone else, like when we are sexting or whatever. He doesn't even ask for me to "tell" him about me and him together anymore. It's always me with someone else, or cheating. I am faithful to him and he is to me as well. That much I know. I have told him before that I don't really like doing this and the other day I really told him that it does hurt me very much thinking that maybe this would change things.
Things did not go as I thought they would. He started to get upset, telling me that he felt bad and saying things like he wishes he could just run (get away from it). He got more and more upset and I felt bad for making him feel that way but I still wanted to show that I was hurt. Well guess what ended up happening? I wanted him to be happy and he said to try something to make him feel better. Yeah. I ended up doing the thing that I hate. All he had to say after was that he was appreciative of me doing that. No apology. He apologized the next day, but it was just for the fact that it made me not sleep well.
Why are my feelings in this not important? Why does he want something that he knows hurts me so incredibly bad? And wants it right after I tell him that it hurts me. I don't know what to do anymore. I love him very much, this is just the one thing that I don't know what to do with. Please help...

I can relate. An ex of mine had this 'fetish' where he wanted me to dominate him sexually...act all demanding and aggressive and say stupid shit that turned me off completely. I told him the scenario didn't do anything for me and actually turned me off to the extent that I just avoided sex at all costs...he agreed to stop...then it started again. Sexual compatibility is very important - eventually you'll just feel gross because you're not being true to yourself, you're undermining your own feelings to appease his. Doesn't work.

He sounds like he is detached from you and you and him together intimately if he needs to get off thinking about other men having sex with you.

Most guys can't stand the thought of a woman they love being even sexually looked at or touched by other men and her possibly enjoying it and not thinking about him.

I had a GF who's BF told her that he didn't want them to have sex in the same room as any of his mates because he didn't want any of them to see her tits or naked body because she was his girl

Then years later he was telling her to strip at a club because the idea of men watching her naked turned him on. One was a man who loved her, later he became a man who used her as masturbation material, IMO.

Some men like the feeling of having to compete, or to feel their partner is desirable to other men.

In the same way, a lion will pursue live prey rather than settle for already dead meat, like a vulture.

I would be more concerned about jealousy because it indicates insecurity.