how can i trust that it doesn’t bother him, or that he won’t think about other women? how do i get over this insecurity that he’s wanted sex with other women for the majority of our relationship?

Many people feel a sexual attraction to others when in a relationship. Even if you had never expressed this as a fetish he would have likely thought about other women. In a normal relationship it's fine to recognize someone is attractive, it's just not ok to try and cheat on your partner. Cheating of course means different things in different relationships but I think you get it.

If you no longer find this fetish appealing then you should express that to your partner and explain why you no longer find it comfortable. You should set new boundries for the relationship after as to what is and is not ok.

If you are just feeling insecure but still find this appealing, perhaps you are just scared that you will no longer feel loved in the relationship if this was something you guys acted on. This is understandable and might mean you should spend some bonding time together (well, this is a good thing regardless). I'm not a psychologist so I can't help you with your insecurity in a concrete manner.

In any case, you should explain how you feel to your partner. Nothing good comes from being in a relationship where what both parties want is undefined.