Okay, "I would marry you tomorrow" is something my ex-husband used to say to me. He was a shitty husband. Why? Because he didn't actually want to be married. He just asked because we had a kid together and his mama told him he should get married. Saying "I do" was the last think he contributed to our relationship. After that, he figured it was a done deal and I should be happy with that.
I don't think you should marry this guy. He doesn't want to be married. It won't work unless he really wants it too.