Besides the complete lack of chemistry, the only thing these two have discussed about getting married is whether not Bella will become a vampire, and if she does, she won't have kids. What's sad is that even the discussion of kids is actually surprising for this movie---in most romances, the happy couple almost never discuss whether or not they want kids. In epilogues of these movies, children are almost always a given. When in reality? Having children is a huge fucking choice and it's not for everyone.
Something that irks me about a lot of romance movies is that couples almost never talk about what they want, besides simply being together. That's nice and all, but you guys are going to have to work as a team. If the two love birds don't want the same things in life (one person wants six kids, the other doesn't), or if their careers or aspirations are taking them in different directions, getting married isn't going to help solve that dilemma. Actually, it probably make it worse, with one partner having to sacrifice their dreams in order to help support the other partner. Which is just a breeding ground for long term resentment and relationship instability.
Like, why can't people in movies just talk? About what they want. What they want for themselves, or together. About communicating, about making choices together, about learning the line of where to put yourself first or your partner. You have to be 110% clear on where you want things. And while this can be hard--and frightening, or embarrassing, if you really love someone, I think, then you're willing to shove through that bull crap and treat them with the same respect you would want them to treat you with, as equals.
Back on engagement: one of my worst fears is a surprise engagement. If someone proposed to me without talking to me about getting married first, I would probably break up with them right then and there. It's inconsiderate and rude. I don't even care if I would get painted as a cold hearted bitch or monster, I don't even care how much time or effort they put into it, I would be furious. Call me unromantic but real life is unromantic. Breaking out champagne and roses and getting engaged without discussing it first isn't a good precedent for when bills are coming in red ink and making major health decisions for our kids. Actually, screw weddings, too, because they're expensive and shitty and everybody hates each other at them, anyways.