You need to reassure him that this inanimate object is not a replacement for him but an addition to your sex life together. You can do this by explaining that a sex toy does not provide love, affection, warmth, romance, support, and all the other things you love about him. Ask him how many women he knows in this wide world that would replace the touch of their partner, the sex with their partner....with an inanimate vibrating object. None of us! Also ask him if he understands that different types of stimulation are just that...different types of stimulation. Ask him if he would enjoy only ever receiving a hand job, despite the fact he knows he COULD experience a blow job too...and the unique feeling of vaginal sex....and the feeling of anal sex....and even the feeling of vibrations or male sex toys. What is wrong with options? Would he limit himself to just one or two types of sensation, even if he knew he could try this and this and this too? and if he did experience a new sensation, would he feel any less for you? Would be suddenly think that your hand jobs, blow jobs and vagina were suddenly useless and not good enough? nope!
Variety is fun. It can spice things up and both partners can benefit from that.
Tell him that you could have orgasm after orgasm with the vibrator, but if he is not there with you, sharing the pleasure and enjoying it with you, then technically it is just a functional orgasm. There is not the same level of excitement. Experiecing orgasms is about bonding with him and enjoying your sex life together and the vibrator is just another tool to do that. part of the excitement comes from knowing he is watching, enjoying, touching you and sharing the experience with you...otherwise it is just an alone orgasm.
If that doesn't work, you need to get firmer and tell him that MOST people masturbate. It is natural and normal. I bet he masturbated before he met you, maybe he still does occasionally....we all do it and is he is going to really deny you a basic human, natural instinct because he feels jealous of the methods you use to get there? Would he make you eat with your hands because the knife and fork make it "too easy"? Would he be jealous if you were one of those women who rubbed herself against a pillow to orgasm? Would he be jealous if you were one of those women who rubbed herself on the arm of a chair, or used a hairbrush, or a vegetable or whatever all of us women have experimented with as we learned to masturbate? Being jealous of the vibrator is the equivilent of telling you that you must orgasm HIS way....the way HE deems acceptable and if you are one of those women who can only reach orgasm from vibrations....how selfish would that be? to deny your partner pleasure just because you cannot handle the fact that it was an inanimate object that works for her.
Anyway. I hope some of that helps you talk to him, reassure him and also stand up for what you should be allowed to experience.....without guilt. xx Good luck