"skittish because of his divorce" says he may need to address that issue first before going further. You are not his ex, and he has to work through that fear and trust you as an individual, not based on his past. Communication is going to be key in the marriage, so upfront and clear needs to start now.
How? A relaxed environment. Dinner, movie, whatever is that happy place for both of you. MayG had a wonderful suggestion--find a movie to ease into the topic--- or "book you've been reading".
From a woman's perspective: We TEND to see marriage as our ultimate reward and outward display of love and commitment. Men don't necessarily see it that way--they feel their presence should be proof enough of love and commitment. If you are doing all the "marital things" together, he sees no real need to potentially muddy the waters with the ceremony and paper. The very act seems to be ominous to the man who wants a sense of choice--or who fears repeating a failed marriage. The reason for the divorce is also a big factor and you would both benefit walking through counseling to ensure he doesn't sabotage the marital success with his fears. (p.s. Counseling can come as a couple's "retreat" so it doesn't seem like a problem, but rather a desire for the next stage of closeness)
Blessings to you Both~