Very brave inquiry. You say you've always felt this way about him. Are you the type of person who is ever animally attracted? Lots of women aren't very "carnivorous" so depending on the personalities of the partners, this happens.
Like, I know women with NO sex drive AT ALL, but since their husbands are super aggressive, the relationship works, because the men do all the seducing and work, and sex happens enough for everyone to feel OK. Other women with the same low sex drive have husbands who are sort of tame and hang back and wait for the wife to "want it" or seduce THEM, and that sort of works, but no one's getting enough lovin'. Or some women are sort of unhorny, and their husbands are too, and then there is no sex life, and sometimes people dont' mind being friends. Other women are super horny, and into their men (rare), and depending on his personality, this usually works well. It's rare for a husband to get sick of his woman wanting him, even if he's totally lazy. And some lucky marriages have two lusty un-lazy people who are attracted to each other.
Would you be a fiery vixon for someone more attractive to you-do you have past emotions like that to back you up? Be sure before you convince yourself you're lacking something.
Does your husband actively come after you, and you just don't want to cooperate? Or does he sort of just leave it up to you 50/50, so you always have to realize you really don't want to make the moves? Have you HAD super lusty attractions to people before? Obsessions, crushes, physical chemistry and butterflies? But just never your husband? Or are you thinking it's something you could have one day, but never have before. If you never have before, it may not be in your wiring. I can remember obsessive crushes as young as 8 years old-and I've always been VERY attracted to people I was with, not always the best thing, but also not many people! When I'm not interested, I'm NOT interested.
The polar opposite of your problem is people so physically attracted, that they end up together and nothing else works. You have a lot of good things.
The sex thing is really going to bug you if you know you would be more lusty for someone else or are already. Or you may just be the mild mannered type to have entered into this under these conditions. We all know what it feels like (or wish we did) to get tingles for the only guy in the room you have a crush on and move heaven and earth to finally pin him down in a marriage. If you NEVER felt that for him, but did for other people, it does seem like religion may have steered you down the righteous path to boredom, but you can still have a rewarding proper life and do the right thing!
It sounds like maybe you're needing someone else to do all the work sexually so you don't have to gear yourself up all the time-and maybe hubby will if you make that clear! The actual act of sex itself isn't going to be a whole lot different for you based on the other person, it's about your entire feelings to make it special.
Ask yourself how you would feel is he lusted after someone else. Would you care? Would you want him more? Are you secretly having crushes on other people which makes you think you don't love him? Try to find what's deep inside yourself....Whatever you do, so NOT say, "I feel trapped" while taking the high road mentality. You are not trapped. If you decide to stay for moral reasons, then you decide that. It's not a trap. Feeling like a victim also builds resentment. Good, luck and I hope you find happiness!