Just talk to her honestly, and if you have to, use the old wonder of logic. Now learn about how all of your doubts can be resolved through apologetics. We met when I was 19 and have been together only the past 4 years but the love has never died. Part of me wants to say Yes!!.
So, kudos to you for having such a wonderful relationship for so long and getting through step 1 and 2 and matching. Will you be open to me teaching my children my athiest point of view. Would she be okay spending a Sunday to an atheist space with you. Interfaith marriage is but one variety of the learning experience.
I knew a Mormon girl who got rides from her Mormon friends for casual sex dates with men she met on Tinder. I also studied his advice for approaching and dating women. I knew a couple in my last ward who got married in their mid 20's. Long story short, everyone is dead on. I find myself oscillating between empathy, pity, and rage, but lately, it's been mostly rage. Then the girl decided still not to date him after all.
However, for me, there have been some perks too. I married outside the church and have no regrets. And as many posters stated, it is something that needs to be seriously discussed with your potential partner. I'll keep digging through it, but there's a lot there and I'd like some suggestions to narrow my search.