Different beliefs

My fiancé and I are engaged to marry. Apparently this whole time he’s been holding out hope for me to convert and be a Christian. He said he really wants it for me and his main reason is getting into heaven. We talked more and he said “I don’t want to lose you for eternity and I want to spend forever with you in heaven”. I mentioned I just don’t think I’ll ever fully be a Christian. I know too much about science and other religions to agree with just one. I’m open to all religions and that’s just how I’ll always be. I respect a lot of his morals that stem from his beliefs but I don’t agree with all of it. He said it broke his heart and it’s hard for him to accept that we may not be together someday, like our lives are already over.

I just really don’t know how to deal with this. He insist that it’s not a deal breaker but I can see it in him how important it was. There’s no more talk of leaving just accepting it and still hoping for the future.

How do I explain that it’s a lost cause to hope for me to convert and devote myself to god?? I feel like I’m just leading him on even though I’ve told him how I feel. Do people with diff religious backgrounds make it work?? And how??? I’ve fully accepted I have no idea what’s in the afterlife and or if there’s a higher power. I try to take in every moment and enjoy it with him and that’s enough for me, why isn’t it for him?? I guess I just don’t understand fully but I don’t want this getting worse for us in the future. Anyone have experience in this??