In many ways, Deadpool is sort of the cousin twice removed of the Marvel Cinematic Universe. He's not invited to the big family reunions, and his relationship to the family is sort of one big mystery. One thing that isn't a mystery though, is whether or not Deadpool 2 is affected by Infinity War. The short answer is no, Deadpool 2 will not be changed much by Avengers: Infinity War. Of course, the long answer is a bit more complicated, but we'll get to that later.
Spoilers ahead. The end of Avengers: Infinity War shook up the MCU in a major way, with Thanos destroying half of the universe's population with a snap of his fingers. And if Deadpool 2 were part of the MCU, that would mean that half of Deadpool's friends would be dead too. Luckily for fans, Deadpool isn't in the MCU. Despite being a Marvel character and property, the Deadpool movies are produced by an entirely different distributors — Fox as opposed to Disney — which means that they simply don't operate in the same world as the movies of the MCU. For all intents and purposes, Deadpool 2 exists in an alternate universe from Infinity War, one without Captain America, the Sokovia Accords, or, yes, even Thanos.
Now, before you think that the case of whether Deadpool 2 will be affected by Infinity War is cut and dry, know that things between the beloved new franchise and the MCU are about to get way more complicated. Late in 2017, it was announced that Disney was in talks of absorbing Fox's movie rights, and with that merger would come all of Fox's Marvel properties including Deadpool. And in December of 2017, Disney announced that it was now the proud owner of all of Fox's film rights. For the small price of $52 billion, Disney bought the rights to X-Men movies, Deadpool, and Fantastic Four, which opens up huge possibilities for the studio and for the MCU. Most notably, it means that more superheroes will have the option of being added into the MCU.
That said, it's unlikely to happen any time soon. The deal between Fox and Disney probably won't be finalized until the end of 2018, so any Deadpool, X-Men, or Fantastic Four additions to the MCU will have to wait at least a few years. And even then, the MCU is famously an intricately planned endeavor, with the next handful of movies already planned out and determined by the studio. As such, figuring out how to merge Deadpool, an already established franchise, into the MCU wouldn't really work out well in the short term.
Marvel Studios President Kevin Feige confirmed as much in an interview with The Playlist, saying that any crossovers or MCU changes from the merger probably wouldn't happen for years. "We're not thinking about that," he said. "We're thinking of delivering on what we promised. Any movie, especially for any characters we don't have the rights to yet until someone tells us we do, would be even further after that." As of 2018, the MCU is booked solid through the early 2020s, so it's likely Deadpool wouldn't be added to the MCU until around 2023 at the earliest.
So, to recap: no, Deadpool 2 won't be affected by Infinity War, and Deadpool is not yet part of the MCU. In fact, it's unclear if Deadpool will ever join the MCU at all. For now, fans should just enjoy the fact that they get to watch more than one superhero universe on the big screen. They don't have to be connected, they just have to be fun.