Your choice of the future here is arbitrary - we could just as easily say that there are many past and present "you" in the multiverse. This assumes a definition closer to DD/DW's than the author's.

The author seems to assert that his experience of self is incongruous with this definition of your identity. As a historical fact, "you've" always either chosen chocolate or vanilla, not both. The other branches aren't in fact you, any longer.