If you attend a wedding with someone, it's natural for people to assume that you are an item. If you're not an item, don't be an awkward turtle when someone asks you how long you two lovebirds have been together. You have a couple of options here. You can deflect with humor: "We're not dating yet, but hopefully we will be by the end of the night." Or you can be earnest: "This is our first big event together…so far, so good." No need to get too into detail about you haven't determined the relationship yet. Just answer and get back on the dance floor.